CBSE Class 10 Science Metals and non metals Sure Shot Questions Set 01

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Question. Which of the following elements is not a metal?
(a) Calcium
(b) Copper
(c) Potassium
(d) Sulphur
Answer: (d) Sulphur

Question. The constituent of haemoglobin is
(a) Iron
(b) Sodium
(c) Copper
(d) Magnesium
Answer: (a) Iron

Question. The lustre of a metal is due to
(a) its high density
(b) its high polishing
(c) its chemical inertness
(d) presence of free electrons
Answer: (d) presence of free electrons

Question. The poorest conductor of heat is
(a) Aluminium
(b) Silver
(c) Gold
(d) Lead
Answer: (d) Lead

Question. The best electrical conductor is
(a) Gold
(b) Copper
(c) Silver
(d) Aluminium
Answer: (c) Silver

1. Which metal is the best conductor of electricity? [1 Mark]

Answer:
1. Silver is the best conductor of electricity.
2. Copper is also an extremely good conductor, but silver ranks first.

Teacher's Note:
a) Silver offers minimum resistance to electric current flow.
b) Copper is commonly used in wires due to cost effectiveness despite silver being slightly better.

2. Which metal is poorest conductor of electricity? [1 Mark]

Answer:
1. Lead is the poorest conductor of electricity among common metals.
2. Mercury also exhibits very poor electrical conductivity compared to other metals.

Teacher's Note:
a) Metals generally conduct electricity well due to free electrons.
b) Lead has significantly higher resistance than silver or copper.

3. Which metal is best conductor of heat ? [1 Mark]

Answer:
1. Silver is the best conductor of heat.
2. Copper is also a very strong thermal conductor.

Teacher's Note:
a) Thermal conductivity in metals is facilitated by free valence electrons.
b) Silver utensils are not commonly used due to high cost.

4. Which metal other than mercury is liquid at room temperature? [1 Mark]

Answer:
1. Gallium is a metal other than mercury that is liquid at room temperature.
2. Caesium also has a very low melting point close to room temperature.

Answer:
1. Lead is considered among the poorest conductors of heat.
2. Mercury is also a poor conductor of heat relative to other metals.

Teacher's Note:
a) Poor thermal conductivity is linked to low free electron mobility efficiency.
b) Bismuth is another metal with relatively low thermal conductivity.

6. What is the nature of oxides of metal? [1 Mark]

Answer:
1. Metallic oxides are generally basic in nature.
2. Some metal oxides like aluminium oxide and zinc oxide are amphoteric.

Teacher's Note:
a) Basic oxides dissolve in water to form metal hydroxides or alkalis.
b) Amphoteric oxides react with both acids and bases.

7. What is the nature of oxides of non- metal? [1 Mark]

Answer:
1. Non-metallic oxides are generally acidic in nature.
2. Some non-metal oxides such as carbon monoxide, water, and nitric oxide are neutral.

Teacher's Note:
a) Acidic non-metal oxides dissolve in water to form acids.
b) Sulfur dioxide and carbon dioxide are classic examples of acidic oxides.

8. Which non-metal conduct electricity? [1 Mark]

Answer:
1. Graphite is the non-metal that conducts electricity.
2. It is an allotrope of carbon.

Teacher's Note:
a) Non-metals are usually poor conductors due to absence of free electrons.
b) Graphite has free electrons in its layered crystal structure.

9. Graphite, allotrope of carbon conduct electricity. [1 Mark]

Answer:
1. Yes, graphite conducts electricity.
2. Each carbon atom in graphite is bonded to three other carbon atoms in the same plane, leaving one free electron per atom.

Teacher's Note:
a) Delocalized electrons move freely throughout the layered structure.
b) This electrical conductivity is unique for a non-metallic substance.

10. Which non-metal is lusturous? [1 Mark]

Answer:
1. Iodine is a lustrous non-metal.
2. Diamond, an allotrope of carbon, also possesses a high degree of luster and brilliance.

Teacher's Note:
a) Non-metals are normally dull in appearance.
b) Iodine crystals have a shining, metallic appearance.

11. Why metals are hard and have high melting point? [2 Marks]

Answer:
1. Metals have strong metallic bonds between metal ions and free electrons.
2. This strong electrostatic attraction requires a large amount of thermal energy to break, resulting in high hardness and high melting points.

Teacher's Note:
a) Metallic bonding holds the crystal lattice tightly together.
b) Alkali metals are exceptions with low melting points and softness.

12. What is an amalgam? [1 Mark]

Answer:
1. An amalgam is an alloy of mercury with another metal.
2. One of the metals is always mercury.

Teacher's Note:
a) Dental amalgams often contain silver and mercury.
b) Iron does not form an amalgam with mercury.

13. What are the constituents of solder? [1 Mark]

Answer:
1. Solder is an alloy of lead and tin.
2. Its chemical constituents are Pb and Sn.

Teacher's Note:
a) Solder has a low melting point.
b) It is commonly used for electrical soldering and joining wires.

14. Name the green coloured compound which appears on the surface of copper utensils? [1 Mark]

Answer:
1. Basic copper carbonate is the green coloured compound.
2. Formula: CuCO₃·Cu(OH)₂.

Teacher's Note:
a) Formed by reaction of copper with moist carbon dioxide and oxygen in air.
b) This process is termed corrosion of copper or tarnishing.

15. Why the item made of silver turns black when exposed to air? [2 Marks]

Answer:
1. Silver reacts with sulfur compounds present in the air such as hydrogen sulfide.
2. This forms a black coating of silver sulfide on the surface.

Teacher's Note:
a) Chemical reaction: 4Ag + 2H₂S + O₂ → 2Ag₂S + 2H₂O.
b) This tarnishing is a form of metallic corrosion.

16. Why do silver ornaments loose their shine when kept for some time? [2 Marks]

Answer:
1. Silver reacts chemically with gaseous components like hydrogen sulfide in the atmosphere.
2. A black layer of silver sulfide accumulates on the jewelry, causing it to lose its lustrous shine.

Teacher's Note:
a) Atmospheric gases react slowly with silver surfaces over time.
b) Polishing or chemical treatment removes this silver sulfide layer.

17. Name a metal other than aluminium that is covered with an oxide film layer. [1 Mark]

Answer:
1. Zinc is a metal covered with a protective oxide layer when exposed to air.
2. Magnesium and chromium also form protective oxide films.

Teacher's Note:
a) Protective oxide layers prevent further oxidation of the underlying metal.
b) This phenomenon is utilized in anodizing processes.

18. Name one metal and one non-metal which exists in liquid state at room temperature? [1 Mark]

Answer:
1. Metal in liquid state: Mercury.
2. Non-metal in liquid state: Bromine.

Teacher's Note:
a) Mercury is the only common liquid metal at room temperature.
b) Bromine is a reddish-brown liquid non-metal.

19. Name a non-metal which is lustrous and a metal which is non-lustrous. [1 Mark]

Answer:
1. Lustrous non-metal: Iodine.
2. Non-lustrous metal: Sodium or Lead (in powdered form).

Teacher's Note:
a) Iodine crystals exhibit a bright characteristic shine.
b) Metals generally have metallic luster, but certain forms or freshly cut surfaces can vary.

20. Name two metal which have very low melting point. [1 Mark]

Answer:
1. Gallium.
2. Caesium.

Teacher's Note:
a) Both metals melt slightly above room temperature.
b) Caesium melts at 28.5°C.

21. If copper metal is heated over a flame, it develops a coating. What is the colour and composition of this coating? [2 Marks]

Answer:
1. Colour of the coating: Black.
2. Composition of the coating: Copper(II) oxide (CuO).

Teacher's Note:
a) Reaction: 2Cu + O₂ → 2CuO.
b) Heating causes copper to combine with oxygen in the air.

22. Why is sodium metal kept immersed in kerosene oil? [2 Marks]

Answer:
1. Sodium is a highly reactive alkali metal.
2. It reacts vigorously with oxygen and moisture in the air, catching fire easily, so it is kept in kerosene to prevent exposure.

Teacher's Note:
a) Sodium does not react with kerosene oil.
b) It is stored under oil for safety reasons.

23. Name one metal which react with very dilute HNO₃ to evolve hydrogen gas. [1 Mark]

Answer:
1. Magnesium (Mg) or Manganese (Mn).
2. These metals react with very dilute nitric acid to produce hydrogen gas.

Teacher's Note:
a) Nitric acid is a strong oxidizing agent which usually oxidizes hydrogen to water.
b) Very dilute HNO₃ at low concentrations reacts with Mg and Mn to evolve H₂.

24. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y, and Z. [3 Marks]

Answer:
1. X is Carbon.
2. Y is Diamond.
3. Z is Graphite.

Teacher's Note:
a) Diamond and graphite are allotropes of carbon.
b) Diamond is extremely hard due to rigid covalent network, while graphite conducts electricity via free electrons.

25. An element A form two oxides AO and AO₂.The oxide AO is neutral whereas the oxide AO₂ is acidic in nature. Would you call element A a metal or non-metal. [2 Marks]

Answer:
1. Element A is a non-metal.
2. Non-metals form neutral or acidic oxides, whereas metals form basic or amphoteric oxides.

Teacher's Note:
a) Carbon forms CO (neutral) and CO₂ (acidic).
b) This confirms element A is a non-metal.

26. In the refining of silver the recovery of silver from silver nitrate solution involves displacement by copper metal. Give the reason for the same. [2 Marks]

Answer:
1. Copper is more reactive than silver.
2. Therefore, copper displaces silver ions from silver nitrate solution, depositing pure silver.

Teacher's Note:
a) Based on the reactivity series, more reactive metals displace less reactive metals.
b) Equation: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag.

27. Name two metals which are both ductile as well as malleable. [1 Mark]

Answer:
1. Gold (Au) and Silver (Ag).
2. Copper and Aluminium are also acceptable answers.

Teacher's Note:
a) Malleability is the ability to be beaten into thin sheets.
b) Ductility is the ability to be drawn into thin wires.

28. The reaction of iron (III) oxide Fe₂O₃ with aluminium is used to join cracked iron parts of machines. [2 Marks]

Answer:
1. This reaction is known as the thermit reaction, which is a highly exothermic displacement reaction.
2. Molten iron is produced in the process due to the large amount of heat evolved.
3. This molten iron is allowed to flow into the cracks of heavy iron machinery or railway tracks to weld them together.
4. Chemical equation: Fe₂O₃(s) + 2Al(s) → Al₂O₃(s) + 2Fe(l) + Heat.

Teacher's Note:
a) Aluminium being more reactive displaces iron from its oxide.
b) Mentioning the term thermit reaction is essential for full credit.

29. Give reason for the following: (a) Ionic compounds conduct electricity in the molten state. [2 Marks]

Answer:
1. Ionic compounds consist of positively and negatively charged ions held together by strong electrostatic forces of attraction.
2. In the solid state, these ions are fixed in their positions and cannot move freely.
3. In the molten state, the electrostatic forces overcome heat energy, allowing ions to move freely and conduct electricity.

Teacher's Note:
a) Free movement of ions is the key requirement for electrical conductivity.
b) Ionic compounds also conduct electricity in aqueous solution for the same reason.

30. Give reason for the following: Metals can be given different shapes according to our needs. [1 Mark]

Answer:
1. Metals possess the property of malleability, meaning they can be beaten into thin sheets.
2. They also possess ductility, allowing them to be drawn into thin wires.

Teacher's Note:
a) Malleability and ductility are characteristic physical properties of metals.

31. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal? [2 Marks]

Answer:
1. The gas liberated is hydrogen gas.
2. Bring a burning candle or matchstick near the opening of the test tube containing the gas.
3. The gas burns with a pop sound, which confirms the presence of hydrogen gas.

Teacher's Note:
a) Hydrogen gas is colorless, odorless, and combustible.
b) The pop sound test is the standard diagnostic test for hydrogen.

32. Which reducing agent is used in the reduction of alumina? [1 Mark]

Answer:
1. Electrolytic reduction (electricity) is used, and no external chemical reducing agent like carbon is used.
2. Aluminium has a high affinity for oxygen, so electrolytic reduction is employed where electrons act as the reducing agent at the cathode.

Teacher's Note:
a) Carbon cannot reduce alumina because aluminium has a higher affinity for oxygen than carbon.

33. What are metalloids? [1 Mark]

Answer:
1. Elements that exhibit properties intermediate between those of metals and non-metals are called metalloids.
2. Examples include boron, silicon, and germanium.

Teacher's Note:
a) They are also known as semimetals.

34. Why are titanium and chromium classified as strategic metals? [2 Marks]

Answer:
1. Titanium and chromium are vital for the defense industry and high-technology applications such as aerospace and nuclear engineering.
2. They possess exceptional strength, low density, and high corrosion resistance under extreme conditions.

Teacher's Note:
a) Their strategic importance stems from their unique combination of high durability and resistance to corrosion.

35. Which one of the following metals does not react with oxygen even at high temperatures? (i) Calcium (ii) Gold (iii) Sodium [1 Mark]

Answer: (ii) Gold

1. Gold is a noble metal placed at the bottom of the reactivity series.
2. It does not react with oxygen even at high temperatures.
3. Hence, the correct option is (ii).

Teacher's Note:
a) Noble metals like gold and platinum do not tarnish or oxidize in air.

36. Give reasons for the following : Addition of some silver to pure gold for making ornaments. [2 Marks]

Answer:
1. Pure gold (24 carat) is very soft and flexible, making it unsuitable for making durable jewellery.
2. Alloying pure gold with a small amount of silver or copper makes it hard and strong, preventing ornaments from bending or deforming easily.

Teacher's Note:
a) 22-carat gold is typically used for making ornaments, containing 22 parts gold and 2 parts copper or silver.

37. Give reason for the following: Alumina is dissolved in molten cryolite for electrolysis to obtain aluminum metal. [2 Marks]

Answer:
1. Pure alumina has a very high melting point and is a poor conductor of electricity.
2. Dissolving alumina in molten cryolite (Na₃AlF₆) lowers its melting point and increases its electrical conductivity.

Teacher's Note:
a) Cryolite acts as a solvent and improves the overall efficiency of the Hall-Héroult process.

38. Write the chemical equation to represent the reaction taking place between sodium metal and cold water. [2 Marks]

Answer:
1. Sodium reacts violently and exothermically with cold water to form sodium hydroxide and hydrogen gas.
2. Chemical equation: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + Heat.

Teacher's Note:
a) The heat evolved during this reaction is sufficient for the hydrogen gas to catch fire.

39. Why is tungsten metal selected for making filaments of incandescent lamp bulbs? [2 Marks]

Answer:
1. Tungsten has a very high melting point (around 3380°C).
2. It does not melt or burn even when heated to a very high temperature due to electric current flow.

Teacher's Note:
a) It also exhibits high tensile strength at high temperatures.

40. Name a metal which offer higher resistance to the passage of electricity than copper. [1 Mark]

Answer:
1. Iron or Nichrome (any one).

Teacher's Note:
a) Copper is an excellent conductor with very low electrical resistivity.

41. Write the chemical equation for the reaction of hot aluminium with steam. [2 Marks]

Answer:
1. Hot aluminium reacts with steam to form aluminium oxide and hydrogen gas.
2. Chemical equation: 2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g).

Teacher's Note:
a) Aluminium does not react with cold or hot water, but reacts vigorously with steam.

42. How does the metal magnesium differ from the metal calcium in their reaction with water? [2 Marks]

Answer:
1. Magnesium does not react with cold water; it reacts only with hot water to form magnesium hydroxide and hydrogen gas, and floats because hydrogen bubbles stick to its surface.
2. Calcium reacts with cold water less violently than sodium, and the metal starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.

Teacher's Note:
a) Both are alkaline earth metals, but calcium is more reactive than magnesium with water.

43. What is seen to happen when a piece of sodium metal is dropped into water? [2 Marks]

Answer:
1. Sodium darts about on the surface of water with a hissing sound.
2. It reacts violently, melts into a silvery ball, and the evolved hydrogen gas catches fire, burning with a yellow flame.

Teacher's Note:
a) Safety precaution: Sodium must be handled with care using forceps.

44. What are amphoteric oxides? Give an example. [2 Marks]

Answer:
1. Metal oxides that react with both acids as well as bases to produce salt and water are called amphoteric oxides.
2. Example: Aluminium oxide (Al₂O₃) or Zinc oxide (ZnO).

Teacher's Note:
a) Most metal oxides are basic in nature, but amphoteric oxides show dual acidic and basic character.

45. Name two metals that react with dil.HNO₃ to evolve H₂ gas ? [1 Mark]

Answer:
1. Magnesium (Mg) and Manganese (Mn).

Teacher's Note:
a) Dilute nitric acid is a strong oxidizing agent which usually oxidizes hydrogen gas to water, but Mg and Mn react with very dilute HNO₃ to evolve H₂ gas.

46. Why metals like potassium and sodium catch fire when treated with water? [2 Marks]

Answer:
1. The reaction of potassium and sodium with water is highly exothermic.
2. The large amount of heat evolved is sufficient for the evolved hydrogen gas to catch fire immediately.

Teacher's Note:
a) These metals are extremely reactive and belong to Group 1 of the periodic table.

47. Why sodium is kept immersed in kerosene oil? [2 Marks]

Answer:
1. Sodium is a highly reactive metal.
2. It reacts vigorously with oxygen and moisture present in the air and can easily catch fire, so it is kept immersed in kerosene oil to cut off contact with air and moisture.

Teacher's Note:
a) Potassium is also stored under kerosene for the same reason.

48. Which gas is produced when dil. HCl is added to a reactive metal? Write the chemical reaction when iron reacts with dil. H₂SO₄? [2 Marks]

Answer:
1. Hydrogen gas is produced.
2. Chemical reaction: Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g).

Teacher's Note:
a) Reactive metals displace hydrogen from dilute acids.

49. What would you observe when zinc is added to a solution of iron(II) sulphate ?write the chemical reaction that takes place. [2 Marks]

Answer:
1. The green color of iron(II) sulphate solution fades and eventually becomes colorless, and a greyish-black coating of iron metal is deposited on zinc.
2. Chemical reaction: Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s).

Teacher's Note:
a) This is a displacement reaction because zinc is more reactive than iron.

50. Why ionic compounds have high melting points? [2 Marks]

Answer:
1. Ionic compounds are composed of oppositely charged ions held together by strong interionic electrostatic forces of attraction.
2. A considerable amount of energy is required to break these strong attractive forces, hence they have high melting points.

Teacher's Note:
a) High melting and boiling points are characteristic physical properties of ionic compounds.

51. What do you mean by roasting? How it is different from calcination? In which types of ores roasting is done? [3 Marks]

Answer:
1. Roasting is the process in which a sulfide ore is strongly heated in the presence of excess air to convert it into its metal oxide.
2. Difference: Roasting is done for sulfide ores in the presence of excess air, whereas calcination is done for carbonate ores in the absence or limited supply of air.
3. Roasting is exclusively done for metal sulfide ores, such as zinc blende (ZnS) or copper pyrite (CuFeS₂).

Teacher's Note:
a) Roasting oxidizes sulfide ores directly to metallic oxides while releasing sulfur dioxide gas.
b) Students often confuse roasting with calcination regarding air supply and ore type.
c) Mentioning balanced chemical equations for roasting is an effective way to secure full marks.

52. Define :- (i) Ore, (ii) Mineral. [2 Marks]

Answer:
1. (i) Ore: Minerals from which metals can be extracted profitably and conveniently are called ores.
2. (ii) Mineral: The naturally occurring elements or compounds in the earth's crust are known as minerals.

Teacher's Note:
a) Remember that all ores are minerals, but all minerals are not ores.
b) Always state profitability and convenience when defining an ore.

53. Name two metals which are found in nature in the free state. [1 Mark]

Answer:
Gold and Silver (or Platinum).

Teacher's Note:
a) Unreactive metals at the bottom of the activity series occur in the native or free state.

54. Define :- (i) Enrichment of Ores (ii) Gangue. [2 Marks]

Answer:
1. (i) Enrichment of Ores: The process of removing unwanted impurities like sand, soil, and rocky substances from the ore is called ore enrichment or concentration.
2. (ii) Gangue: The large amount of unwanted rocky impurities, sand, and earthy particles associated with an ore is called gangue.

Teacher's Note:
a) Enrichment increases the percentage of metal in the extracted ore before smelting.
b) Gangue must be separated using physical or chemical methods prior to reduction.

55. Write short notes on electrolytic refining of metals. [3 Marks]

Answer:
1. Electrolytic refining is the process of purifying impure metals using electricity.
2. The impure metal is made the anode and a thin strip of pure metal is made the cathode in an electrolytic cell containing a soluble metal salt solution.
3. On passing electric current, pure metal from the anode dissolves into the electrolyte and gets deposited on the cathode, leaving soluble impurities in solution and insoluble impurities as anode mud.

Teacher's Note:
a) Commonly used for refining copper, zinc, tin, and nickel.
b) Impurities like gold and silver settle down as anode mud below the anode.
c) The electrolyte is usually an acidified solution of the metal salt being refined.

56. Name the conditions which are essential for corrosion. [2 Marks]

Answer:
1. Presence of moisture (water or water vapor).
2. Presence of oxygen (air).

Teacher's Note:
a) Both oxygen and water must be present simultaneously for rusting or corrosion to occur.
b) Acidic gases in the atmosphere can accelerate the rate of corrosion.

57. What is Galvanisation? Write its use. [2 Marks]

Answer:
1. Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
2. It is used extensively to protect iron and steel objects from rusting, such as in making water pipes and iron sheets.

Teacher's Note:
a) Zinc prevents oxygen and moisture from coming in contact with the underlying iron.
b) Zinc acts as a sacrificial anode because it oxidizes more easily than iron.

58. Write suitable example, explain how a metal low in the activity series can be extracted? [3 Marks]

Answer:
1. Metals low in the activity series are very unreactive and their oxides can be reduced to metals by heating alone.
2. Example: Cinnabar (HgS) is an ore of mercury; on heating, it is first converted into mercuric oxide (HgO).
3. Mercuric oxide when heated further gets reduced to mercury metal: \(2HgO_{(s)} \rightarrow 2Hg_{(l)} + O_{2(g)}\).

Teacher's Note:
a) Metals like gold, silver, and platinum are found in native state, while mercury and copper are obtained by thermal decomposition of their oxides or sulfides.
b) No external reducing agents like carbon are required for these low-reactivity metals.
c) Mentioning physical states in the chemical reaction adds precision.

59. Write three properties of ionic compounds. [3 Marks]

Answer:
1. Physical Nature: Ionic compounds are solid and hard due to strong forces of attraction between positive and negative ions.
2. Melting and Boiling Points: They have high melting and boiling points because a considerable amount of energy is required to break the strong inter-ionic attraction.
3. Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents like kerosene and petrol.

Teacher's Note:
a) Mention electrical conductivity as an alternative property if needed.
b) Ionic compounds conduct electricity in molten or aqueous state due to free ions.
c) Solid ionic compounds do not conduct electricity because ions are rigidly fixed in crystal lattices.

60. What is anodizing? What is its use? [2 Marks]

Answer:
1. Anodizing is a process of forming a thick oxide layer of aluminium that protects it from further corrosion.
2. Use: It is used to make aluminium articles corrosion-resistant and capable of being dyed easily in attractive colors.

Teacher's Note:
a) Aluminium develops a thin oxide layer naturally, which is made thicker artificially during anodizing.
b) The clean aluminium article is made the anode in dilute sulfuric acid during the electrolytic process.

61. What is aqua regia? What is its use? [2 Marks]

Answer:
1. Aqua regia is a freshly prepared 3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid.
2. Use: It is used for dissolving noble metals like gold and platinum, which do not dissolve in ordinary acids.

Teacher's Note:
a) It is a highly corrosive and fuming liquid also known as royal water.
b) It can convert inert metals into soluble metal chlorides.

62. What do you mean by thermite reaction? What is its use? [2 Marks]

Answer:
1. The thermite reaction is a highly exothermic displacement reaction between iron (III) oxide and aluminium powder.
2. Use: The huge amount of heat evolved melts the iron metal, which is used to join railway tracks or cracked machine parts.

Teacher's Note:
a) Reaction equation: \(Fe_{2}O_{3} + 2Al \rightarrow 2Fe + Al_{2}O_{3} + Heat\).
b) Highly reactive metals like aluminium displace metals of lower reactivity from their oxides.

63. Why active metals do not liberate H2 gas when treated with dil. HNO3? [2 Marks]

Answer:
1. Nitric acid (HNO₃) is a strong oxidizing agent.
2. When active metals react with dil. HNO₃, it oxidizes the hydrogen gas produced to form water and itself gets reduced to nitrogen oxides.

Teacher's Note:
a) Magnesium and manganese are exceptions that react with very dilute HNO₃ to liberate hydrogen gas.
b) Emphasize the strong oxidizing property of nitric acid in the answer.

64. Sometimes the ore itself acts as a reducing agent. Give an example. [2 Marks]

Answer:
1. In the extraction of certain metals, the unreacted metal sulfide ore reacts with its roasted oxide or sulfate form to reduce itself to the metal without an external reducing agent.
2. Example: In the extraction of copper, copper sulfide reacts with copper oxide: \(2Cu_{2}O + Cu_{2}S \rightarrow 6Cu + SO_{2}\).

Teacher's Note:
a) This self-reduction process is characteristic of semi-precious metal extraction like copper, lead, and mercury.
b) The sulfur in the ore effectively drives out the oxygen as sulfur dioxide gas.

65. An alkali metal A gives a compound B (molecular mass=40) on reacting with water .The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B, and C and give the reaction involved. [3 Marks]

Answer:
1. Compound B has molecular mass 40, which corresponds to sodium hydroxide (NaOH), since Na = 23, O = 16, H = 1 = 40.
2. Therefore, alkali metal A is Sodium (Na), compound B is Sodium hydroxide (NaOH), and compound C formed with aluminium oxide is Sodium aluminate (\(NaAlO_{2}\)).
3. Reactions involved:
\(2Na + 2H_{2}O \rightarrow 2NaOH + H_{2}\)
\(Al_{2}O_{3} + 2NaOH \rightarrow 2NaAlO_{2} + H_{2}O\)

Teacher's Note:
a) Use molecular mass calculations as a clue to identify compound B as NaOH.
b) Sodium is an alkali metal that reacts vigorously with cold water.
c) Aluminium oxide is amphoteric, reacting with sodium hydroxide to form soluble sodium aluminate.

66. An element A burns with golden flame in air .It reacts with another element B, atomic number 17 to give a product C .An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen .Identify A, B, C and D. Also write down the equations for the reactions involved. [4 Marks]

Answer:
1. Element A burning with golden yellow flame is Sodium (Na).
2. Element B with atomic number 17 is Chlorine (Cl).
3. Product C formed by reaction of A and B is Sodium chloride (NaCl).
4. Compound D formed during the chlor-alkali electrolysis of aqueous NaCl is Sodium hydroxide (NaOH), along with hydrogen and chlorine gas.
5. Reactions involved:
\(4Na + O_{2} \rightarrow 2Na_{2}O\)
\(2Na + Cl_{2} \rightarrow 2NaCl\) (Product C)
\(2NaCl_{(aq)} + 2H_2O_{(l)} \rightarrow 2NaOH_{(aq)} + Cl_{2(g)} + H_{2(g)}\) (Compound D is NaOH)

Teacher's Note:
a) Golden yellow flame is the characteristic flame test color for sodium compounds.
b) Atomic number 17 corresponds to chlorine, forming sodium chloride (common salt).
c) The electrolysis of aqueous sodium chloride is known as the chlor-alkali process.
d) Ensure all chemical equations are properly balanced with physical states.

67. A metal which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature .Identify the metal and its ore and give the reaction involved. [3 Marks]

Answer:
1. The metal used in the thermite process is Aluminium (Al).
2. The ore of aluminium is Bauxite (\(Al_{2}O_{3}\cdot 2H_{2}O\)).
3. Oxide B is Aluminium oxide (\(Al_{2}O_{3}\)), which is amphoteric.
4. Reaction: \(4Al + 3O_{2} \rightarrow 2Al_{2}O_{3}\)

Teacher's Note:
a) Aluminium is a reactive metal that forms an amphoteric oxide when heated with oxygen.
b) Bauxite is the primary commercial ore of aluminium.
c) Amphoteric oxides react with both acids and bases to form salt and water.

68. Give reasons
(i) Copper is used to make hot water tanks but steel is not.
(ii) Tarnished copper vessels being cleaned with lemon or tamarind juice.
(iii) Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters.
(iv) A salt which does not conduct electricity in the solid state becomes a good conductor in molten state
(v) Why ionic compounds have high melting points?
(vi) Why sodium is kept immersed in kerosene oil?
(vii) Why metals like potassium and sodium catch fire when treated with water?
(viii) Why metals are hard and have high melting point? [4 Marks]

Answer:
1. (i) Copper does not react with water or steam at any temperature, whereas steel (an alloy of iron) reacts with hot water and steam, leading to rapid rusting.
2. (ii) Tarnished copper vessels have a coating of basic copper carbonate, which is basic in nature. Lemon or tamarind juice contains acids that neutralize the basic layer and dissolve it, cleaning the vessel.
3. (iii) Metal sulfides are insoluble and stable in rocks, whereas metal halides like sodium chloride are highly soluble in water and get washed into seas and oceans.
4. (iv) In the solid state, ions are held tightly by strong electrostatic forces and cannot move. In the molten state, electrostatic forces are overcome by heat, freeing the ions to conduct electricity.
5. (v) Ionic compounds have high melting points because strong inter-ionic electrostatic forces hold the oppositely charged ions together, requiring a large amount of thermal energy to break.
6. (vi) Sodium is a very reactive metal that catches fire spontaneously if exposed to moisture and oxygen in the air. Kerosene prevents contact with air and moisture.
7. (vii) Potassium and sodium react violently and exothermically with water, liberating hydrogen gas which immediately catches fire due to the heat evolved.
8. (viii) Metals have strong metallic bonding where valence electrons are shared collectively, binding metal ions tightly together and resulting in high hardness and melting points.

Teacher's Note:
a) Address each sub-part with specific scientific principles such as reactivity, neutralization, solubility, and bonding.
b) Students must clearly distinguish between physical states and chemical reactivity in reasons.
c) Use chemical terms like electrostatic attraction, basic carbonate, and exothermic reactions to gain full credit.
d) Verify that all eight sub-parts are answered concisely in corresponding order.

69. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen. [3 Marks]

Answer:
1. The metal M is copper (Cu) because it is less reactive than hydrogen and does not displace it from dilute acids.
2. The black coloured product is copper (II) oxide (CuO).
3. When copper is heated in air, it reacts with oxygen to form copper (II) oxide: 2Cu + O₂ → 2CuO.

Teacher's Note:
a) Copper sits below hydrogen in the reactivity series, hence no hydrogen gas is evolved with acids.
b) A common student mistake is confusing copper oxide (black) with copper carbonate (green).
c) This is a classic oxidation reaction where a reddish-brown metal turns black upon heating.

70. Given below are the steps for extraction of copper from its ore .Write the reaction involved [3 Marks]
(i)Roasting of copper (I) sulphide.
(ii)Reduction of copper (I) oxide with copper (1) sulphide.
(iii) Draw a neat and well labelled diagram for electrolytic refining of copper.

Answer:
1. Roasting: 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
2. Reduction: 2Cu₂O + Cu₂S → 6Cu + SO₂
3. Electrolytic refining diagram:

Teacher's Note:
a) Roasting converts sulphide ores into oxides using excess air.
b) Self-reduction occurs when copper oxide reacts with remaining copper sulphide without external reducing agents.
c) Impure copper forms the anode and pure copper forms the cathode during refining.

71. A metal is found in liquid state in nature .It is less reactive than hydrogen .It occurs as sulphide ore .Describe the reactions how can we extract this metal from its ore .Name the ore also. [3 Marks]

Answer:
1. The metal is mercury (Hg) and its ore is cinnabar (HgS).
2. Roasting of ore: 2HgS + 3O₂ → 2HgO + 2SO₂
3. Thermal reduction: 2HgO → 2Hg + O₂

Teacher's Note:
a) Mercury is the only metal that exists as a liquid at room temperature.
b) Cinnabar is heated in air to first convert it into mercuric oxide.
c) Mercuric oxide is unstable on heating and readily reduces to metallic mercury.

72. Explain why [4 Marks]
(i) Aluminium cannot be extracted by reducing alumina with carbon.
(ii)Concentrated HNO₃ can be stored in aluminum containers.
(iii)Aluminium is used for making transmission wires.
(iv) 24 carat gold cannot be used for making ornaments.

Answer:
1. Aluminium has a very high affinity for oxygen, higher than carbon, so carbon cannot reduce alumina.
2. Concentrated nitric acid renders aluminium passive by forming a thin protective layer of aluminium oxide on its surface.
3. Aluminium is a good conductor of electricity and is lightweight and cheap compared to copper.
4. Pure 24 carat gold is extremely soft and flexible, making it unsuitable for durable ornaments without alloying.

Teacher's Note:
a) Electrolytic reduction is required for highly reactive metals like aluminium.
b) Oxide film formation prevents further chemical reaction with acid.
c) Alloying gold with copper or silver gives it the required strength.

73. Which of the following property is generally not shown by metals? [1 Mark]
(a) Electrical conduction
(b) Sonorous in nature
(c) Dullness
(d) Ductility

Answer: (C) Dullness

1. Metals are lustrous and shiny, not dull.
2. Hence, the correct option is (C).

Teacher's Note:
a) Physical properties of metals include high lustre, conductivity, and ductility.

74. The ability of metals to be drawn into thin wire is known as [1 Mark]
(a) ductility
(b) malleability
(c) sonorousity
(d) conductivity

Answer: (A) ductility

1. Ductility is the specific property allowing metals to be drawn into wires.
2. Hence, the correct option is (A).

Teacher's Note:
a) Do not confuse ductility with malleability, which is beating into sheets.

75. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same? [1 Mark]
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) High melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)

Answer: (D) (i) and (iv)

1. Cooking utensils require high thermal conductivity to heat food quickly and a high melting point so they do not melt during cooking.
2. Hence, the correct option is (D).

Teacher's Note:
a) Electrical conductivity and ductility are not primary reasons for making cooking pots.

76. Which of the following property is generally not shown by metals? [1 Mark]
(a) Electrical conduction
(b) Sonorous in nature
(c) Dullness
(d) Ductility

Answer: (C) Dullness

1. Metals possess metallic lustre and are shiny.
2. Hence, the correct option is (C).

Teacher's Note:
a) This is a repeated question testing metal appearance.

77. The ability of metals to be drawn into thin wire is known as [1 Mark]
(a) ductility
(b) malleability

(c) sonorousity
(d) conductivity

Answer: (A) ductility

1. Drawing into thin wires defines ductility.
2. Hence, the correct option is (A).

Teacher's Note:
a) Basic definition question from physical properties of metals.

78. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same? [1 Mark]
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) High melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)

Answer: (d) (i) and (iv)

1. Aluminium has high thermal conductivity, which allows heat to pass through it quickly for cooking.
2. It also has a high melting point, preventing the utensil from melting easily at high temperatures.
3. Electrical conductivity and ductility are not the primary reasons for making cooking utensils.
4. Hence, the correct option is (d).

Teacher's Note:
a) Utensils require heat transfer properties rather than electrical conductivity.
b) High melting point ensures structural integrity under continuous heating.

79. Which one of the following metals do not react with cold as well as hot water? [1 Mark]
(a) Na
(b) Ca
(c) Mg
(d) Fe

Answer: (d) Fe

1. Sodium (Na) and calcium (Ca) react with cold water.
2. Magnesium (Mg) reacts with hot water.
3. Iron (Fe) does not react with either cold or hot water, but reacts only with steam.
4. Hence, the correct option is (d).

Teacher's Note:
a) Reactivity with water decreases down the reactivity series.
b) Iron requires high-temperature steam to form iron oxide and hydrogen gas.

80. Which of the following oxide(s) of iron would be obtained on prolonged reaction of iron with steam? [1 Mark]
(a) FeO
(b) Fe₂O₃
(c) Fe₃O₄
(d) Fe₂O₃ and Fe₃O₄

Answer: (c) Fe₃O₄

1. Metals like aluminium, iron, and zinc do not react either with cold or hot water.
2. However, they react with steam to form the metal oxide and hydrogen.
3. The reaction of iron with steam produces magnetic iron oxide, Fe₃O₄, along with hydrogen gas.
4. Hence, the correct option is (c).

Teacher's Note:
a) Fe₃O₄ is a mixed oxide containing both FeO and Fe₂O₃.
b) This reaction is reversible under specific industrial conditions.

81. What happens when calcium is treated with water? [1 Mark]
(i) It does not react with water
(ii) It reacts violently with water
(iii) It reacts less violently with water
(iv) Bubbles of hydrogen gas formed stick to the surface of calcium
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)

Answer: (d) (iii) and (iv)

1. Calcium reacts with water less violently than sodium or potassium.
2. The heat evolved is not sufficient for the hydrogen to catch fire.
3. The bubbles of hydrogen gas formed stick to the surface of the metal.
4. As a result, calcium starts floating on water; hence, statements (iii) and (iv) are correct.

Teacher's Note:
a) Calcium floats because hydrogen gas bubbles adhere to its surface.
b) The reaction is exothermic but less vigorous compared to alkali metals.

82. Generally metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)? [1 Mark]
(a) H₂SO₄
(b) HCl
(c) HNO₃
(d) All of these

Answer: (c) HNO₃

1. Nitric acid (HNO₃) is a strong oxidizing agent.
2. When metals react with HNO₃, the nitric acid oxidizes the hydrogen gas produced to water and itself gets reduced to nitrogen oxides.
3. Manganese (Mn) and magnesium (Mg) are exceptions that react with very dilute HNO₃ to evolve hydrogen gas.
4. Hence, the correct option is (c).

Teacher's Note:
a) Strong oxidizing property of nitric acid prevents hydrogen gas evolution.
b) Mn and Mg react with extremely dilute nitric acid to produce H₂.

83. The composition of aqua-regia is [1 Mark]
(a) Dil.HCl : Conc.HNO₃ :: 3 : 1
(b) Conc.HCl : Dil.HNO₃ :: 3 : 1
(c) Conc.HCl : Conc.HNO₃ :: 3 : 1
(d) Dil.HCl : Dil.HNO₃ :: 3 : 1

Answer: (c) Conc.HCl : Conc.HNO₃ :: 3 : 1

1. Aqua-regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1.
2. It is a highly corrosive, fuming liquid.
3. It can dissolve gold and platinum, even though neither acid can do so alone.
4. Hence, the correct option is (c).

Teacher's Note:
a) The ratio must be strictly 3 parts concentrated HCl to 1 part concentrated HNO₃.
b) It generates nascent chlorine which attacks noble metals.

84. Which of the following are not ionic compounds? [1 Mark]
(i) KCl
(ii) HCl

(iii) CCl₄
(iv) NaCl
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iii)

Answer: (b) (ii) and (iii)

1. Potassium chloride (KCl) is formed by the transfer of electrons from potassium to chlorine, making it an ionic compound.
2. Hydrogen chloride (HCl) is formed by the sharing of electrons between hydrogen and chlorine, making it a covalent compound.
3. Therefore, HCl is not an ionic compound.
4. CCl₄ is also a covalent compound, formed by sharing of electrons. Hence, the correct option is (b) (ii) and (iii).

Teacher's Note:
a) Ionic compounds conduct electricity in molten or aqueous state due to free ions.
b) Covalent compounds like dry HCl gas do not dissociate into ions.

85. Which one of the following properties is not generally exhibited by ionic compounds? [1 Mark]
(A) Solubility in water
(B) Electrical conductivity in solid state
(C) High melting and boiling points
(D) Electrical conductivity in molten state

Answer: (B) Electrical conductivity in solid state

1. Ionic compounds are generally soluble in water and have high melting and boiling points due to strong inter-ionic forces.
2. In the solid state, ions are held in a rigid crystal lattice and are not free to move, so they do not conduct electricity.
3. In the molten state or in aqueous solution, ionic compounds conduct electricity because their ions become free.
4. Hence, the correct option is (B).

Teacher's Note:
a) Ionic compounds conduct electricity only in molten or dissolved states.
b) Solid ionic compounds are insulators because ions lack mobility.
c) Remember that electrostatic forces of attraction are very strong in solids.

86. Which of the following metals exist in their native state in nature? [1 Mark]
(i) Cu
(ii) Au
(iii) Zn
(iv) Ag
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)

Answer: (c) (ii) and (iv)

1. Metals at the bottom of the reactivity series are least reactive and exist in a free or native state.
2. Gold (Au) and Silver (Ag) are unreactive noble metals that are found in native form in nature.
3. Copper and Zinc are moderately reactive and usually occur as oxides, sulphides, or carbonates.
4. Hence, the correct option is (c) (ii) and (iv).

Teacher's Note:
a) Native state metals are chemically inert and do not react easily with air or moisture.
b) Silver sometimes occurs natively, though often combined; gold is strictly native.
c) Highly and moderately reactive metals form compounds.

87. Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining? [1 Mark]
(i) Au
(ii) Cu
(iii) Na
(iv) K
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iii) and (iv)

Answer: (c) (ii) and (iii)

1. Electrolytic refining is widely used to purify copper (Cu), zinc, tin, nickel, silver, and gold.
2. Highly reactive metals like sodium (Na) and potassium (K) are obtained by electrolytic reduction of their molten chlorides.
3. Therefore, both copper and sodium are processed or refined using electrolytic methods.
4. Hence, the correct option is (c) (ii) and (iii).

Teacher's Note:
a) Electrolytic refining involves impure metal as anode and pure metal as cathode.
b) Highly reactive alkali metals are extracted via electrolysis of molten salts.
c) Note that the official key combines Cu and Na as standard curriculum examples for electrolytic processes.

88. Silver articles become black on prolonged exposure to air. This is due to the formation of [1 Mark]
(A) Ag₃N
(B) Ag₂O
(C) Ag₂S
(D) Ag₂S and Ag₃N

Answer: (C) Ag₂S

1. Silver reacts with sulphur compounds present in the air, such as hydrogen sulphide gas.
2. This chemical reaction produces a black coating of silver sulphide (Ag₂S) on the metal surface.
3. The process is commonly known as the tarnishing of silver.
4. Hence, the correct option is (C).

Teacher's Note:
a) Silver does not react with oxygen at room temperature to form oxides in air.
b) Trace sulphur gases in the atmosphere cause black tarnish.
c) Chemical formula for silver sulphide is Ag₂S.

89. Galvanisation is a method of protecting iron from rusting by coating with a thin layer of [1 Mark]
(A) Gallium
(B) Aluminium
(C) Zinc
(D) Silver

Answer: (C) Zinc

1. Galvanisation is the process of applying a protective zinc coating to steel or iron.
2. The zinc layer prevents corrosive substances from reaching the underlying steel or iron structure.
3. Zinc also acts as a sacrificial anode, protecting the iron even if the coating is scratched.
4. Hence, the correct option is (C).

Teacher's Note:
a) Galvanisation specifically uses zinc metal.
b) It prevents contact with oxygen and moisture to stop rusting.
c) Sacrificial protection is a key advantage of zinc over other coatings.

90. Stainless steel is very useful material for our life. In stainless steel, iron is mixed with [1 Mark]
(A) Ni and Cr
(B) Cu and Cr
(C) Ni and Cu
(D) Cu and Au

Answer: (A) Ni and Cr

1. Stainless steel is an alloy of iron with carbon, chromium, and nickel.
2. Chromium provides corrosion resistance, while nickel improves strength and ductility.
3. Copper and gold are not standard alloying elements for stainless steel.
4. Hence, the correct option is (A).

Teacher's Note:
a) Stainless steel is an important corrosion-resistant alloy.
b) Iron is alloyed with chromium (Cr) and nickel (Ni).
c) Alloys alter physical properties like hardness and rusting tendency.

91. If copper is kept open in air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of [1 Mark]
(A) CuSO₄
(B) CuCO₃
(C) Cu(NO₃)₂
(D) CuO

Answer: (B) CuCO₃

1. Moist copper reacts with carbon dioxide in the air over time.
2. This slow reaction forms a green-coloured basic copper carbonate, which is a mixture of copper hydroxide and copper carbonate.
3. The green coating is commonly referred to as basic copper carbonate, represented by CuCO₃ in simplified options.
4. Hence, the correct option is (B).

Teacher's Note:
a) Weathered copper forms a green patina layer.
b) The reaction involves moisture, carbon dioxide, and oxygen.
c) Basic copper carbonate formula is often tested in board examinations.

92. Generally, metals are solid in nature. Which one of the following metals is found in liquid state at room temperature? [1 Mark]
(a) Na
(b) Fe
(c) Cr
(d) Hg

Answer: (d) Hg

1. Most metals exist as solids at room temperature due to strong metallic bonding.
2. Mercury (Hg) is a d-block transition element that has a very low melting point (-38.83 °C).
3. Hence, mercury is the only common metal that remains in liquid state at room temperature, and the correct option is (d).

Teacher's Note:
a) Mercury is widely used in thermometers due to its high coefficient of expansion and wide temperature range.
b) Sodium (Na) is a soft solid, iron (Fe) and chromium (Cr) are hard transition metals.

93. Which of the following metals are obtained by electrolysis of their chlorides in molten state ? [1 Mark]
(i) Na
(ii) Ca
(iii) Fe
(iv) Cu
(a) (i) and (iv)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (i) and (ii)

Answer: (d) (i) and (ii)

1. Highly reactive metals at the top of the reactivity series, such as sodium (Na) and calcium (Ca), have a very high affinity for oxygen and chlorine.
2. They cannot be reduced using carbon because their oxides or chlorides are more stable than carbon monoxide.
3. Therefore, they are extracted by the electrolytic reduction of their molten chlorides.
4. Hence, the correct option is (d).

Teacher's Note:
a) Iron (Fe) is extracted by reduction with carbon (blast furnace), and copper (Cu) is obtained by self-reduction or electrolytic refining.
b) Sodium and calcium are liberated at the cathode during the electrolysis of their molten salts.

94. Generally, non-metals are not lustrous. Which of the following nonmetal is lustrous? [1 Mark]
(a) Sulphur
(b) Oxygen
(c) Nitrogen
(d) Iodine

Answer: (d) Iodine

1. Non-metals are generally dull in appearance and do not possess a shiny surface.
2. Iodine is an exception as it exists as purple-black lustrous crystals with a shiny metallic-like appearance.
3. Hence, the correct option is (d).

Teacher's Note:
a) Lustre is a physical property typically characteristic of metals due to free mobile electrons reflecting light.
b) Iodine shows weak metallic character in its physical appearance despite being a halogen non-metal.

95. Which one of the following four metals would be displaced from the solution of its salts by other three metals? [1 Mark]
(a) Mg
(b) Ag
(c) Zn
(d) Cu

Answer: (b) Ag

1. A more reactive metal can displace a less reactive metal from its salt solution based on the reactivity series.
2. Silver (Ag) is at the bottom of the reactivity series, below magnesium, zinc, and copper.
3. Consequently, silver can be displaced by all the other three metals (Mg, Zn, Cu) from its salt solution.
4. Hence, the correct option is (b).

Teacher's Note:
a) The reactivity series places metals in order of decreasing chemical reactivity.
b) Silver is a noble metal and does not easily react with dilute acids or displace other metal ions.

96. 2 mL each of concentrated HCl, HNO₃ and a mixture of concentrated HCl and concentrated HNO₃ in the ratio of 3 : 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be [1 Mark]
(a) Al
(b) Au
(c) Cu
(d) Pt

Answer: (c) Cu

1. Test tube C contains aqua regia, which is a 3:1 mixture of concentrated HCl and concentrated HNO₃.
2. Aqua regia is a strong oxidizing agent capable of dissolving noble metals like gold and platinum, as well as less reactive transition metals like copper.
3. Copper does not dissolve in concentrated HCl (test tube A) or concentrated HNO₃ alone under certain passive conditions, but it readily dissolves in aqua regia (test tube C).
4. Hence, the correct option is (c).

Teacher's Note:
a) Aqua regia translates to royal water and fumes heavily with a yellow-orange color.
b) Gold (Au) and platinum (Pt) dissolve in aqua regia, but option (c) copper is the standard school-level answer for this specific textbook question.

97. An alloy is [1 Mark]
(a) an element
(b) a compound
(c) a homogeneous mixture
(d) a heterogeneous mixture

Answer: (c) a homogeneous mixture

1. An alloy is a solid solution of two or more metals, or a metal and a non-metal.
2. Its components are uniformly distributed throughout its mass at the microscopic level.
3. Therefore, an alloy exhibits properties of a homogeneous mixture.
4. Hence, the correct option is (c).

Teacher's Note:
a) Brass and bronze are classic examples of solid homogeneous metallic alloys.
b) Alloys often possess better tensile strength and corrosion resistance than their pure constituent elements.

98. An electrolytic cell consists of
(i) positively charged cathode
(ii) negatively charged anode
(iii) positively charged anode
(iv) negatively charged cathode
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (ii) ad (iv)

Answer: (b) (iii) and (iv)

1. In an electrolytic cell, electrical energy drives a non-spontaneous chemical reaction.
2. The anode is connected to the positive terminal of the power supply, making it positively charged (iii), where oxidation occurs.
3. The cathode is connected to the negative terminal of the power supply, making it negatively charged (iv), where reduction occurs.
4. Hence, the correct option is (b).

Teacher's Note:
a) Remember the rule: Anode is positive and Cathode is negative in electrolytic cells (whereas in galvanic cells, the anode is negative).
b) Cations migrate toward the negative cathode, and anions migrate toward the positive anode.

99. During electrolytic refining of zinc, it gets [1 Mark]
(A) deposited on cathode
(B) deposited on anode
(C) deposited on cathode as well as anode
(D) remains in the solution

Answer: (A) deposited on cathode

1. In electrolytic refining, impure metal is made the anode and a pure strip of metal is made the cathode.
2. On passing electric current, metal ions from the electrolyte are reduced by gaining electrons at the cathode.
3. Pure zinc gets deposited on the cathode.
4. Hence, the correct option is (A).

Teacher's Note:
a) Cathode is always made of pure metal during electrolytic refining.
b) Impure metal dissolves from the anode into the electrolyte solution.

100. An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following [1 Mark]
(A) Mg
(B) Na
(C) P
(D) Ca

Answer: (B) Na

1. Alkali metals like sodium are soft and can be cut with a knife.
2. Sodium (Na) reacts vigorously with moisture and oxygen in the air, catching fire if kept open.
3. It reacts violently with water to form sodium hydroxide and hydrogen gas.
4. Hence, the correct option is (B).

Teacher's Note:
a) Sodium is stored under kerosene to prevent accidental contact with air and moisture.
b) Magnesium and calcium are harder and less reactive than sodium.

101. Alloys are homogeneous mixtures of a metal with a metal or nonmetal. Which among the following alloys contain non-metal as one of its constituents? [1 Mark]
(A) Brass
(B) Bronze
(C) Amalgam
(D) Steel

Answer: (D) Steel

1. Steel is an alloy of iron and carbon, where carbon is a non-metal.
2. Brass is an alloy of copper and zinc (both metals).
3. Bronze is an alloy of copper and tin (both metals).
4. Hence, the correct option is (D).

Teacher's Note:
a) Carbon is added in small amounts to iron to make it hard and strong.
b) Amalgams always contain mercury alloyed with another metal.

102. Which among the following statements is incorrect for magnesium metal? [1 Mark]
(A) It burns in oxygen with a dazzling white flame
(B) It reacts with cold water to form magnesium oxide and evolves hydrogen gas
(C) It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
(D) It reacts with steam to form magnesium hydroxide and evolves hydrogen gas

Answer: (B) It reacts with cold water to form magnesium oxide and evolves hydrogen gas

1. Magnesium does not react with cold water.
2. It reacts only with hot water to form magnesium hydroxide and hydrogen gas.
3. Statement (B) is factually incorrect because magnesium does not react with cold water.
4. Hence, the correct option is (B).

Teacher's Note:
a) Magnesium floats on water due to hydrogen gas bubbles sticking to its surface.
b) Always check the physical state of water specified in metal-water reaction questions.

103. Which among the following alloys contain mercury as one of its constituents? [1 Mark]
(A) Stainless steel
(B) Alnico
(C) Solder
(D) Zinc amalgam

Answer: (D) Zinc amalgam

1. An amalgam is defined as an alloy of mercury with another metal.
2. Zinc amalgam is formed by mixing zinc with mercury.
3. Solder is an alloy of lead and tin.
4. Hence, the correct option is (D).

Teacher's Note:
a) Mercury is a liquid metal at room temperature, which dissolves solid metals to form amalgams.
b) Solder has a low melting point and is used for welding electrical wires.

104. Reaction between X and Y, forms compound Z. X loses electron and Y gains electron. Which of the following properties is not shown by Z? [1 Mark]
(A) Has high melting point
(B) Has low melting point
(C) Conducts electricity in molten state
(D) Occurs as solid

Answer: (B) Has low melting point

1. Since X loses electrons and Y gains electrons, compound Z is an ionic compound.
2. Ionic compounds have strong electrostatic forces of attraction between oppositely charged ions.
3. Therefore, they possess high melting and boiling points, not low melting points.
4. Hence, the correct option is (B).

Teacher's Note:
a) Ionic compounds are generally solid and hard due to strong inter-ionic attraction.
b) They conduct electricity only in molten or aqueous state, not in solid state.

105. The electronic configurations of three elements X, Y and Z are X - 2, 8; Y - 2, 8, 7 and Z - 2, 8, 2. Which of the following is correct? [1 Mark]
(A) X is a metal
(B) Y is a metal
(C) Z is a non-metal
(D) Y is a non-metal and Z is a metal

Answer: (D) Y is a non-metal and Z is a metal

1. Element X has configuration 2, 8 (Atomic number 10, Neon, a noble gas).
2. Element Y has configuration 2, 8, 7 (Atomic number 17, Chlorine, a non-metal with 7 valence electrons).
3. Element Z has configuration 2, 8, 2 (Atomic number 12, Magnesium, a metal with 2 valence electrons).
4. Hence, the correct option is (D).

Teacher's Note:
a) Elements with 1, 2 or 3 valence electrons are typically metals.
b) Elements with 5, 6 or 7 valence electrons are typically non-metals.

106. Although metals form basic oxides, which of the following metals form an amphoteric oxide? [1 Mark]
(A) Na
(B) Ca
(C) Al
(D) Cu

Answer: (C) Al

1. Aluminium (Al) forms aluminium oxide (\(\text{Al}_2\text{O}_3\)), which reacts with both acids and bases to produce salt and water.
2. Therefore, aluminium oxide is an amphoteric oxide.
3. Sodium and calcium form basic oxides, while copper forms a basic oxide.
4. Hence, the correct option is (C).

Teacher's Note:
a) Zinc and aluminium are classic examples of metals that form amphoteric oxides.
b) Amphoteric oxides show both acidic and basic characteristics.

107. Generally, non-metals are not conductors of electricity. Which of the following is a good conductor of electricity? [1 Mark]
(a) Diamond
(b) Graphite
(c) Sulphur
(d) Fullerene

Answer: (b) Graphite

1. Graphite is an allotrope of carbon in which each carbon atom is bonded to three other carbon atoms in the same plane.
2. This leaves one free valence electron per carbon atom, making it mobile and able to conduct electricity.
3. Hence, the correct option is (b).

Teacher's Note:
a) Graphite has free electrons that enable electrical conduction.
b) Diamond lacks free electrons and is a poor conductor.

108. Electrical wires have a coating of an insulating material. The material, generally used is [1 Mark]
(a) Sulphur
(b) Graphite
(c) PVC
(d) All can be used

Answer: (c) PVC

1. Electrical wires require a protective coating of an insulator to prevent electric shocks and short circuits.
2. PVC (Polyvinyl chloride) is a good plastic insulator commonly used for this purpose.
3. Hence, the correct option is (c).

Teacher's Note:
a) Insulators resist the flow of electric current.
b) Graphite is a conductor and sulphur is brittle and unsuited for wire coatings.

109. Which of the following non-metals is a liquid? [1 Mark]
(a) Carbon
(b) Bromine
(c) Phosphorus
(d) Sulphur

Answer: (b) Bromine

1. Bromine is a halogen belonging to the non-metal group.
2. At room temperature, it exists in a liquid state.
3. Hence, the correct option is (b).

Teacher's Note:
a) Mercury is the only metal liquid at room temperature, while bromine is the only liquid non-metal.
b) Carbon, phosphorus, and sulphur are solids at room temperature.

110. Which of the following can undergo a chemical reaction? [1 Mark]
(a) \(\text{MgSO}_4 + \text{Fe}\)
(b) \(\text{ZnSO}_4 + \text{Fe}\)
(c) \(\text{MgSO}_4 + \text{Pb}\)
(d) \(\text{CuSO}_4 + \text{Fe}\)

Answer: (d) \(\text{CuSO}_4 + \text{Fe}\)

1. A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution.
2. Iron (Fe) is more reactive than copper (Cu), so it displaces copper from copper sulphate solution.
3. Magnesium and zinc are more reactive than iron, lead, etc., hence iron, zinc and lead cannot displace magnesium.
4. Hence, the correct option is (d).

Teacher's Note:
a) Refer to the reactivity series of metals to determine displacement feasibility.
b) Iron sits below magnesium and zinc, but above copper in the reactivity series.

111. Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions. [3 Marks]

Answer:
1. The gas produced in both reactions is hydrogen gas (\(\text{H}_2\)).
2. Identification: Bring a burning matchstick near the gas bubbles; it burns with a pop sound.
3. Reaction with sodium hydroxide: \(\text{M} + 2\text{NaOH} \rightarrow \text{Na}_2\text{MO}_2 + \text{H}_2\) (where M can be Zinc, producing Sodium Zincate and Hydrogen gas).
4. Reaction with hydrochloric acid: \(\text{M} + 2\text{HCl} \rightarrow \text{MCl}_2 + \text{H}_2\).

Teacher's Note:
a) Amphoteric metals like zinc react with both acids and bases to liberate hydrogen gas.
b) The pop sound test is a standard confirmatory test for hydrogen gas.
c) Divalent means the element has a valency of 2.

112. During extraction of metals, electrolytic refining is used to obtain pure metals.
(a) Which material will be used as anode and cathode for refining of silver metal by this process?
(b) Suggest a suitable electrolyte also.
(c) In this electrolytic cell, where do we get pure silver after passing electric current? [3 Marks]

Answer:
(a) Anode: Impure silver block; Cathode: A thin strip of pure silver.
(b) Electrolyte: An acidified aqueous solution of a silver salt, such as silver nitrate (\(\text{AgNO}_3\)).
(c) Pure silver is deposited at the cathode after passing the electric current.

Teacher's Note:
a) During electrolytic refining, metal from the anode dissolves into the electrolyte.
b) An equivalent amount of pure metal from the electrolyte is deposited on the cathode.
c) Soluble impurities go into the solution, while insoluble impurities settle down at the bottom of the anode as anode mud.

113. Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them? [2 Marks]

Answer:
1. It is much easier to obtain a metal from its oxide form than from its sulphide or carbonate form through reduction.
2. Therefore, metal sulphides and carbonates are first converted to metal oxides by roasting and calcination respectively before reduction.

Teacher's Note:
a) Reduction of metal oxides using carbon or other reducing agents is a thermodynamically viable and efficient process.
b) Roasting involves heating in the presence of excess air, while calcination involves heating in a limited supply of air.

114. Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO3, hydrogen is not liberated, why? [2 Marks]

Answer:
1. Nitric acid (\(\text{HNO}_3\)) is a strong oxidizing agent.
2. It oxidizes the hydrogen gas produced to water and itself gets reduced to any of the nitrogen oxides (\(\text{NO}_2\), \(\text{NO}\), or \(\text{N}_2\text{O}\)).

Teacher's Note:
a) Very dilute nitric acid can react with magnesium and manganese to liberate hydrogen gas.
b) Regular mineral acids like hydrochloric acid do not act as strong oxidising agents.

115. Compound X and aluminium are used to join railway tracks.
(a) Identify the compound X
(b) Name the reaction
(c) Write down its reaction. [3 Marks]

Answer:
(a) Compound X is Iron(III) oxide (Ferric oxide, \(\text{Fe}_2\text{O}_3\)).
(b) The reaction is known as the Thermit reaction.
(c) Chemical equation: \(\text{Fe}_2\text{O}_3(s) + 2\text{Al}(s) \rightarrow 2\text{Fe}(l) + \text{Al}_2\text{O}_3(s) + \text{Heat}\).

Teacher's Note:
a) Highly exothermic displacement reactions are used where metals displace lower metals from their oxides.
b) Molten iron is produced in this reaction which fills the gaps of cracked railway tracks.
c) Aluminium acts as a reducing agent in this process.

116. When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved. [3 Marks]

Answer:
1. Molecular mass of \(\text{XOH} = 40 \implies \text{Atomic mass of X} + 16 (\text{O}) + 1 (\text{H}) = 40 \implies \text{Atomic mass of X} = 23\).
2. The metal X is Sodium (Na).
3. The basic salt Y is Sodium Hydroxide (\(\text{NaOH}\)).
4. The gas Z is Hydrogen (\(\text{H}_2\)), which catches fire due to the high exothermic nature of the reaction.
5. Chemical equation: \(2\text{Na}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{NaOH}(aq) + \text{H}_2(g) + \text{Heat}\).

Teacher's Note:
a) Alkali metals react vigorously with cold water to form hydroxides and hydrogen gas.
b) Use molar masses to deduce the identity of unknown elements from given molecular formulas.
c) Hydrogen gas is extremely flammable and catches fire from the heat released in the reaction.

117. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z. [3 Marks]

Answer:
1. X is Carbon.
2. Y is Diamond, which is an allotrope of carbon and the hardest natural substance known.
3. Z is Graphite, which is an allotrope of carbon and a good conductor of electricity.

Teacher's Note:
a) Allotropy is the property of an element to exist in two or more different physical forms.
b) Diamond is hard due to its rigid tetrahedral network structure.
c) Graphite conducts electricity due to the presence of free mobile electrons in its layered structure.

118. The following reaction takes place when aluminium powder is heated with MnO2:
3 MnO2 (s) + 4 Al (s) → 3 Mn (l) + 2 Al2O3 (l) + Heat
(a) Is aluminium getting reduced?
(b) Is MnO2 getting oxidised? [2 Marks]

Answer:
1. (a) No, aluminium is not getting reduced; it is getting oxidised to Al2O3 as it gains oxygen.
2. (b) No, MnO2 is not getting oxidised; it is getting reduced to Mn as it loses oxygen.

Teacher's Note:
a) Oxidation is the gain of oxygen or loss of electrons.
b) Reduction is the loss of oxygen or gain of electrons.

119. What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires? [2 Marks]

Answer:
1. The constituents of solder alloy are lead (Pb) and tin (Sn).
2. Solder has a very low melting point, which makes it suitable for welding electrical wires.

Teacher's Note:
a) Alloys are homogeneous mixtures of two or more metals or a metal and a non-metal.
b) The low melting point of solder allows it to melt easily without damaging sensitive electronic components.

120. A metal A, which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH. [3 Marks]

Answer:
1. Metal A is Aluminium (Al) and Oxide B is Aluminium oxide (Al2O3).
2. Reaction with HCl: Al2O3 + 6 HCl → 2 AlCl3 + 3 H2O
3. Reaction with NaOH: Al2O3 + 2 NaOH → 2 NaAlO2 + H2O

Teacher's Note:
a) Aluminium is used in thermite welding due to its high reactivity and exothermic displacement reactions.
b) Amphoteric oxides are metal oxides that react with both acids and bases to form salt and water.
c) Check balancing of chemical equations carefully.

121. A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved. [3 Marks]

Answer:
1. The metal is Mercury (Hg) and its ore is Cinnabar (HgS).
2. Roasting of ore: 2 HgS (s) + 3 O2 (g) → 2 HgO (s) + 2 SO2 (g)
3. Thermal reduction: 2 HgO (s) → 2 Hg (l) + O2 (g)

Teacher's Note:
a) Mercury is the only metal that is liquid at room temperature.
b) Cinnabar is heated in air (roasting) to convert metal sulphide directly to its oxide, which then thermally decomposes.

122. Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.
(a) Mg and N2
(b) Li and O2
(c) Al and Cl2
(d) K and O2 [2 Marks]

Answer:
1. (a) Mg3N2 (Magnesium nitride)
2. (b) Li2O (Lithium oxide)
3. (c) AlCl3 (Aluminium chloride)
4. (d) K2O (Potassium oxide)

Teacher's Note:
a) Binary compounds are formed by the combination of two different elements by balancing their valencies.
b) Ensure proper cross-multiplication of valencies to write correct chemical formulae.

123. What happens when
(a) ZnCO3 is heated in the absence of oxygen?
(b) a mixture of Cu2O and Cu2S is heated? [2 Marks]

Answer:
1. (a) Zinc carbonate undergoes calcination to form zinc oxide and carbon dioxide: ZnCO3 (s) → ZnO (s) + CO2 (g)
2. (b) Copper(I) oxide and copper(I) sulphide react to form copper metal and sulphur dioxide gas: 2 Cu2O + Cu2S → 6 Cu + SO2

Teacher's Note:
a) Calcination is the process of heating a carbonate ore in the absence of air.
b) Self-reduction occurs when copper sulphide reduces copper oxide in the extraction of copper.

124. A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming
(a) Identify A, B and C
(b) To which Group of Periodic Table does A belong? [2 Marks]

Answer:
1. (a) A is Carbon, B is Carbon monoxide (CO), and C is Carbon dioxide (CO2).
2. (b) Carbon belongs to Group 14 of the Periodic Table.

Teacher's Note:
a) Carbon is an essential element found in all organic compounds in our food (carbohydrates, proteins, fats).
b) Carbon monoxide is toxic because it binds strongly to haemoglobin in blood.

125. Give two examples each of the metals that are good conductors and poor conductors of heat respectively. [1 Mark]

Answer:
1. Good conductors of heat: Silver and Copper.
2. Poor conductors of heat: Lead and Mercury.

Teacher's Note:
a) Metals are generally good conductors of heat and electricity, but there are notable variations.

126. Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C). [2 Marks]

Answer:
1. Liquid metal: Mercury; Liquid non-metal: Bromine.
2. Metals with melting point less than 310 K: Gallium and Caesium.

Teacher's Note:
a) Gallium and Caesium have such low melting points that they melt if kept on the palm of a hand.

127. An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved. [3 Marks]

Answer:
1. A is Calcium (Ca), B is Calcium hydroxide (Ca(OH)2), and C is Calcium oxide (CaO).
2. Reaction of A with water: Ca + 2 H2O → Ca(OH)2 + H2
3. Heating of B: Ca(OH)2 → CaO + H2O; Reaction of C with water: CaO + H2O → Ca(OH)2

Teacher's Note:
a) Calcium oxide is commonly known as quicklime and calcium hydroxide is slaked lime.
b) Slaked lime is extensively used for white washing walls.

128. An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved. [3 Marks]

Answer:
1. A is Sodium (Na), B is Sodium hydroxide (NaOH), and C is Sodium aluminate (NaAlO2).
2. Reaction with water: 2 Na + 2 H2O → 2 NaOH + H2
3. Reaction with aluminium oxide: Al2O3 + 2 NaOH → 2 NaAlO2 + H2O

Teacher's Note:
a) Sodium hydroxide has a molar mass of 23 + 16 + 1 = 40 g/mol.
b) Alkali metals react vigorously with water to form strong alkalis and hydrogen gas.

129. Give the reaction involved during extraction of zinc from its ore by
(a) roasting of zinc ore
(b) calcination of zinc ore [2 Marks]

Answer:
1. (a) Roasting of zinc sulphide (zinc blende): 2 ZnS (s) + 3 O2 (g) → 2 ZnO (s) + 2 SO2 (g)
2. (b) Calcination of zinc carbonate (calamine): ZnCO3 (s) → ZnO (s) + CO2 (g)

Teacher's Note:
a) Roasting is performed on sulphide ores in the presence of excess air.
b) Calcination is performed on carbonate ores in the absence or limited supply of air.

130. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen. [3 Marks]

Answer:
1. Metal M is Copper (Cu).
2. The black coloured product is Copper (II) oxide or cupric oxide (CuO).
3. When copper metal is heated strongly in air, it reacts with oxygen to form a black coloured copper (II) oxide.
4. Chemical equation: 2Cu + O₂ → 2CuO (Black)

Teacher's Note:
a) Copper is less reactive than hydrogen, so it does not displace hydrogen from dilute acids.
b) Ensure the balancing of the chemical equation for the oxidation of copper.
c) A common mistake is confusing CuO (black) with Cu₂O (red).

131. An element forms an oxide A₂O₃ which is acidic in nature. Identify A as a metal or non-metal. [1 Mark]

Answer:
1. The element A is a non-metal.
2. Non-metals generally form acidic oxides or neutral oxides.

Teacher's Note:
a) Metallic oxides are basic or amphoteric in nature, whereas non-metallic oxides are acidic or neutral.
b) Check the valence of A in A₂O₃ to confirm group valency.

132. A solution of CuSO₄ was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved. [3 Marks]

Answer:
1. Iron is more reactive than copper, so it displaces copper from copper sulphate solution.
2. As iron continuously dissolves to form ferrous sulphate, the iron pot gets consumed and develops holes.
3. Chemical equation: Fe + CuSO₄ → FeSO₄ + Cu

Teacher's Note:
a) Reactivity series principle governs single displacement reactions.
b) Students often forget to mention the colour change from blue to light green.
c) Mentioning the formation of ferrous sulphate is essential for full credit.

133. A non-metal A which is the largest constituent of air, when heated with H₂ in 1:3 ratio in the presence of catalyst (Fe) gives a gas B. On heating with O₂ it gives an oxide C. If this oxide is passed into water in the presence of air it gives an acid D which acts as a strong oxidising agent.
(a) Identify A, B, C and D
(b) To which group of periodic table does this non-metal belong? [3 Marks]

Answer:
1. (a) A is Nitrogen (N₂), B is Ammonia (NH₃), C is Nitrogen dioxide (NO₂) or Nitric oxide reacting further, and D is Nitric acid (HNO₃).
2. (b) Nitrogen belongs to Group 15 of the periodic table.

Teacher's Note:
a) Haber's process is used for the manufacture of ammonia (gas B).
b) Nitric acid acts as a strong oxidising agent due to the release of nascent oxygen.
c) Connect air composition knowledge with industrial chemical synthesis steps.

134. Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores. [3 Marks]

Answer:
1. For low reactivity metals (sulphide ores): Roasting of the sulphide ore in the presence of air to convert it into metal oxide, followed by thermal reduction.
2. For medium reactivity metals (sulphide ores): Roasting is carried out to convert the sulphide ore into its corresponding metal oxide.
3. Reduction of the metal oxide to metal using a reducing agent like carbon, followed by electrolytic or chemical refining.

Teacher's Note:
a) Roasting involves heating strongly in the presence of excess air.
b) Do not confuse roasting with calcination, which is done for carbonate ores.
c) Mention reducing agents explicitly for medium reactivity metals.

135. Explain the following
(a) Reactivity of Al decreases if it is dipped in HNO₃
(b) Carbon cannot reduce the oxides of Na or Mg
(c) NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
(d) Iron articles are galvanised.
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature. [5 Marks]

Answer:
1. (a) Concentrated nitric acid is a strong oxidising agent; it forms a thin passive protective layer of aluminium oxide on the surface which prevents further reaction.
2. (b) Sodium and magnesium have a very high affinity for oxygen compared to carbon, hence carbon cannot reduce their oxides.
3. (c) In solid NaCl, ions are held together by strong electrostatic forces and cannot move freely, whereas in molten or aqueous state, ions become free to conduct electricity.
4. (d) Galvanisation involves coating iron with a layer of zinc to protect it from rusting and corrosion.
5. (e) These metals are highly reactive and readily react with oxygen, moisture, and carbon dioxide in nature to form compounds.

Teacher's Note:
a) Passive layer formation protects aluminium from corrosion effectively.
b) High reactivity metals must be extracted by electrolytic reduction rather than chemical reduction.
c) Mobility of ions is the fundamental condition for electrical conduction in ionic compounds.
d) Mention sacrificial protection in galvanisation for better clarity.

136. Given below are the steps for extraction of copper from its ore. Write the reaction involved.
(a) Roasting of copper (1) sulphide
(b) Reduction of copper (1) oxide with copper (1) sulphide.
(c) Electrolytic refining [3 Marks]

Answer:
1. (a) 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
2. (b) 2Cu₂O + Cu₂S → 6Cu + SO₂
3. (c) At cathode: Cu²⁺ + 2e^- → Cu; At anode: Cu → Cu²⁺ + 2e^-

Teacher's Note:
a) Auto-reduction occurs when copper (I) oxide reacts with remaining copper (I) sulphide.
b) Impure copper acts as anode and pure copper acts as cathode during electrolytic refining.
c) Acidified copper sulphate solution is used as the electrolyte.

137. Draw a neat and well labelled diagram for electrolytic refining of copper [3 Marks]

Answer:
1. Set up a tank containing acidified copper sulphate solution as electrolyte.
2. Connect the impure copper rod to the positive terminal (anode) and a thin strip of pure copper to the negative terminal (cathode) of a battery.
3. Pass electric current so that pure copper from the electrolyte deposits on the cathode and impurities settle down as anode mud.

Teacher's Note:
a) Ensure correct polarity: Anode is positive (impure metal), Cathode is negative (pure metal).
b) Anode mud contains valuable impurities like silver, gold, and platinum.
c) Label electrolyte composition (copper sulphate solution + dilute sulphuric acid) clearly.

138. Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity. [3 Marks]

Answer:
1. Metal X is Sodium or Potassium (reacts with cold water).
2. Metal Y is Magnesium (reacts with hot water).
3. Metal Z is Aluminium, Iron or Zinc (reacts with steam only).
4. Order of increasing reactivity: Z < Y < X

Teacher's Note:
a) Reaction with water depends directly on the metal's position in the reactivity series.
b) Cold water reactors are most reactive, while steam reactors have moderate to low reactivity.
c) Verify the increasing order symbol direction carefully.

139. An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D. Also write down the equations for the reactions involved. [5 Marks]

Answer:
1. Element A is Sodium (Na) as it burns with a golden yellow flame.
2. Element B with atomic number 17 is Chlorine (Cl₂).
3. Product C is Sodium Chloride (NaCl).
4. Compound D is Sodium Hydroxide (NaOH).
5. Chemical equations: 2Na + Cl₂ → 2NaCl; 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

Teacher's Note:
a) Flame test characteristic helps identify sodium instantly.
b) Chlor-alkali process is represented by the electrolysis of aqueous sodium chloride.
c) Balance all reactions carefully including state symbols wherever necessary.

140. Two ores A and B were taken. On heating ore A gives CO₂ whereas, ore B gives SO₂. What steps will you take to convert them into metals? [3 Marks]

Answer:
1. Ore A gives CO₂ on heating, which means it is a carbonate ore; it needs to be processed by calcination (heating in the absence of air) to form metal oxide.
2. Ore B gives SO₂ on heating, which means it is a sulphide ore; it needs to be processed by roasting (heating strongly in the presence of air) to form metal oxide.
3. Finally, the metal oxides obtained from both ores are reduced using suitable reducing agents like carbon to obtain free metals.

Teacher's Note:
a) Calcination is done in limited air or absence of air for carbonates.
b) Roasting is done in excess air for sulphide ores.
c) Reduction of metal oxide is the final common step to get the pure metal.

Question. A metal which melts on the palm is
(a) Potassium
(b) Sodium
(c) Gallium
(d) Phosphorous
Answer: (c) Gallium

Question. Which of the following metals form amphoteric oxide?
(a) Copper
(b) Silver
(c) Aluminium
(d) Iron
Answer: (c) Aluminium

Question. Complete the reaction: \( Zn + 2NaOH \to \)
(a) \( Zn(OH)_2 + H_2 \)
(b) \( Na_2ZnO_2 + H_2 \)
(c) \( Zn(OH)_2 + Na_2O \)
(d) \( Na_2ZnO_2 + Na_2O \)
Answer: (b) \( Na_2ZnO_2 + H_2 \)

Question. An element 'X' form an oxide \( XO_2 \), which is a very useful gas used in photosynthesis process. The element is
(a) Sulphur
(b) Nitrogen
(c) Carbon
(d) Phosphorus
Answer: (c) Carbon

Question. The acid formed when sulphur trioxide reacts with water is
(a) Sulphurous acid
(b) Sulphuric acid
(c) Both (a) and (b)
(d) None of the options
Answer: (b) Sulphuric acid

Question. Which of the following elements produces basic oxide on reacting with oxygen?
(a) Chlorine
(b) Sulphur
(c) Phosphorus
(d) Magnesium
Answer: (d) Magnesium

Question. Which of the following metals is protected even by a layer of its oxide?
(a) Copper
(b) Silver
(c) Iron
(d) Aluminium
Answer: (d) Aluminium

Question. Which of the following metals is protected from oxygen and moisture by immersing in kerosene oil?
(a) Potassium
(b) Magnesium
(c) Aluminium
(d) Silver
Answer: (a) Potassium

Question. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be -
(a) Calcium
(b) Carbon
(c) Silicon
(d) Iron
Answer: (a) Calcium

Question. The white phosphorus is stored-
(a) in air
(b) under water
(c) under kerosene
(d) under \( CS_2 \)
Answer: (b) under water

Question. The metal that reacts with cold water is
(a) Mercury
(b) Sodium
(c) Zinc
(d) Tungsten
Answer: (b) Sodium

Question. \( Zn + H_2O \text{ (Steam)} \to A + B \). In the equation A and B are -
(a) \( Zn, H \) only
(b) \( ZnH_2 \text{ and } O_2 \)
(c) \( ZnO_2 \text{ & } O_2 \)
(d) \( ZnO \text{ & } H_2 \)
Answer: (d) \( ZnO \text{ & } H_2 \)

Question. The reactivities of iron, magnesium, sodium and zinc towards water are in the following order
(a) \( Fe > Mg > Na > Zn \)
(b) \( Zn > Na > Mg > Fe \)
(c) \( Na > Mg > Zn > Fe \)
(d) \( Mg > Na > Fe > Zn \)
Answer: (c) \( Na > Mg > Zn > Fe \)

Question. When metal Z is added to dilute HCl solution, there is no evolution of gas. Metal is
(a) K
(b) Na
(c) Ag
(d) Zn
Answer: (c) Ag

Question. An alloy of zinc and copper is dissolved in dilute hydrochloric acid. Hydrogen gas is evolved. In this evolution of gas
(a) only zinc reacts with dilute hydrochloric acid
(b) only copper reacts with dilute hydrochloric acid
(c) both zinc and copper react with dilute hydrochloric acid
(d) only copper reacts with water
Answer: (a) only zinc reacts with dilute hydrochloric acid

Question. \( Cu + HCl \to \)
(a) react vigorously
(b) no reaction
(c) react moderately
(d) react slowly
Answer: (b) no reaction

Question. Copper sulphate solution can be safely kept in a container made of
(a) Aluminium
(b) Lead
(c) Silver
(d) Zinc
Answer: (c) Silver

Question. Beakers A, B and C contain zinc sulphate, silver sulphate and iron (II) sulphate solutions respectively. Copper pieces are added to each beaker. Blue colour will appear in case of
(a) beaker A
(b) beaker B
(c) beaker C
(d) All the beakers
Answer: (b) beaker B

Question. Which of the following reactions cannot occur?
(a) \( 2AgNO_3(aq) + Fe(s) \to Fe(NO_3)_2(aq) + 2Ag(s) \)
(b) \( CuSO_4(aq) + Zn(s) \to ZnSO_4(aq) + Cu(s) \)
(c) \( CuSO_4(aq) + 2Ag(s) \to Cu(s) + Ag_2SO_4(aq) \)
(d) \( 2AgNO_3(aq) + Zn(s) \to Zn(NO_3)_2(aq) + 2Ag(s) \)
Answer: (c) \( CuSO_4(aq) + 2Ag(s) \to Cu(s) + Ag_2SO_4(aq) \)

Question. A student puts one big iron nail each in four test tubes containing solutions of zinc sulphate, aluminium sulphate, copper sulphate and iron sulphate. A reddish-brown coating was observed only on the surface of iron nail which was put in the solution of
(a) Zinc sulphate
(b) Iron sulphate
(c) Copper sulphate
(d) Aluminium sulphate
Answer: (c) Copper sulphate

Question. The reaction \( Cu^{2+}(aq) + Zn(s) \to Zn^{2+}(aq) + Cu(s) \), indicates that the metal which appears lower in the reactivity series is
(a) Zn
(b) Cu
(c) \( Zn^{2+} \)
(d) \( Cu^{2+} \)
Answer: (b) Cu

Question. Identify the pair of metals which reacts with conc. \( HNO_3 \) to liberate hydrogen gas?
(a) Cu, Zn
(b) Cu, Mg
(c) Mg, Mn
(d) Zn, Mn
Answer: (c) Mg, Mn

Question. Which of the following pairs will give displacement reactions?
(a) \( ZnSO_4 \) solution and Aluminium metal
(b) \( MgCl_2 \) solution and Aluminium metal
(c) \( FeSO_4 \) solution and Silver metal
(d) \( NaNO_3 \) solution and Copper metal
Answer: (a) \( ZnSO_4 \) solution and Aluminium metal

Question. Non metals generally contain........ electrons in their outer most shell
(a) 1, 2 or 3
(b) 5, 6, 7 and 8
(c) 10 to 18
(d) 8, 9 or 10
Answer: (b) 5, 6, 7 and 8

Question. Metal always found in free state is
(a) gold
(b) silver
(c) copper
(d) sodium
Answer: (a) gold

Question. Cinnabar is an ore of
(a) Hg
(b) Cu
(c) Pb
(d) Zn
Answer: (a) Hg

Question. Which of the following is an oxide ore?
(a) Bauxite
(b) Cuprite
(c) Haematite
(d) All of the options
Answer: (d) All of the options

Question. All ores are minerals while all minerals are not ores because
(a) the metal cannot be extracted economically from all the minerals
(b) minerals are complex compounds
(c) minerals are obtained from mines
(d) All of the options
Answer: (a) the metal cannot be extracted economically from all the minerals

Question. The impurities present in an ore are known by the name
(a) Flux
(b) Ore
(c) Gangue
(d) Slag
Answer: (c) Gangue

Question. Which of the following ores is best concentrated by froth floatation method?
(a) Galena
(b) Cassiterite
(c) Magnetite
(d) Malachite
Answer: (a) Galena

Question. Which one of the following is not a method of concentration of metal ores?
(a) Gravity separation
(b) Froth floatation process
(c) Electromagnetic separation
(d) Smelting
Answer: (d) Smelting

Question. Which one of the following ore is not concentrated by froth floatation process?
(a) Copper pyrites
(b) Copper glance
(c) Rock salt
(d) Zinc blende
Answer: (c) Rock salt

Question. The process of removing lighter gangue particles by washing in a current of water is called
(a) levigation
(b) liquation
(c) leaching
(d) cupellation
Answer: (a) levigation

Question. Gravity separation method is based upon
(a) preferential washing of ores and gangue particles
(b) difference in densities of ore particles and impurities
(c) difference in chemical property of ore particles and impurites
(d) None of the options
Answer: (b) difference in densities of ore particles and impurities