CBSE Class 10 Science Metals and Non Metals MCQs Set 12

Answer: (c) Malleability

Explanation:
1. Beating a metal into thin sheets is called malleability.
2. Ductility is drawing into wires, and sonority is producing a ringing sound, so only (c) fits.

Teacher's Note:
1. Link the word with the action: malleable means hammered into sheets.
2. Aluminium foil is a daily-life example.

Answer: (c) PVC

Explanation:
1. Sulphur is brittle and is not used for coating wires, and graphite conducts electricity.
2. PVC is a flexible plastic that does not conduct electricity, so it is used as the insulating coating.

Teacher's Note:
1. Insulators protect us from electric shock.
2. Graphite is a conductor, so it cannot be an insulator.

Answer: (a) Carbon is the most malleable metal.

Explanation:
1. Carbon is a non-metal and is not malleable, so statement (a) is false.
2. Copper conducts electricity, aluminium conducts heat and bromine is the only liquid non-metal, so (b), (c) and (d) are true.

Teacher's Note:
1. Carbon is not a metal at all.
2. Gold and silver are the most malleable metals.

Answer: (b) Graphite and iodine

Explanation:
1. Graphite and iodine are the two non-metals that look shiny.
2. Phosphorus, sulphur and chlorine are not lustrous.

Teacher's Note:
1. Remember graphite and iodine as lustrous non-metals.
2. Chlorine is a yellow-green gas.

Answer: (d) Lead

Explanation:
1. Silver, gold and aluminium are good conductors of heat.
2. Lead is a poor conductor of heat.

Teacher's Note:
1. Silver is the best conductor.
2. Lead and mercury conduct heat poorly.

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

Explanation:
1. Aqua regia (royal water) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid.
2. The ratio is 3 : 1 by volume, so the answer is (c).

Teacher's Note:
1. Three parts HCl to one part HNO3, both concentrated.
2. It can dissolve gold and platinum.

Answer: (b) Au

Explanation:
1. The mixture in test tube C is aqua regia, which dissolves noble metals such as gold.
2. Gold is not attacked by concentrated HCl or concentrated HNO₃ separately, so Au fits. Al, Cu and Zn would react with at least one of the acids alone.

Teacher's Note:
1. Only aqua regia dissolves gold and platinum.
2. The other metals react with one of the single acids.

Answer: (c) CO

Explanation:
1. Fe₂O₃ is basic, Al₂O₃ is amphoteric and NO₂ is acidic.
2. CO is neutral. It does not change the colour of litmus.

Teacher's Note:
1. Neutral oxides include CO, NO, N2O and water.
2. Learn one example for each type of oxide.

Answer: (c) silver

Explanation:
1. Aluminium, lead and zinc are more reactive than copper and would displace copper from its solution.
2. Silver is less reactive than copper, so it does not react and the container is safe.

Teacher's Note:
1. The container metal must be less reactive than the dissolved metal.
2. Otherwise displacement slowly eats up the container.

Answer: (c) copper sulphate

Explanation:
1. Iron is less reactive than zinc and aluminium, so it does not displace them, and it cannot displace itself.
2. Iron displaces copper from copper sulphate: Fe + CuSO₄ → FeSO₄ + Cu. The reddish-brown coating is copper.

Teacher's Note:
1. Reddish-brown deposit means copper metal.
2. The solution also turns from blue to pale green.

Answer: (a) Cu and AgNO₃ solution

Explanation:
1. Copper is more reactive than silver, so it displaces silver from AgNO₃ solution.
2. Silver cannot displace iron, copper cannot displace sodium and magnesium cannot displace sodium from NaCl solution.

Teacher's Note:
1. Check that the free metal is more reactive than the metal in the salt.
2. Sodium is more reactive than Mg and Cu.

Answer: (c) It catches fire and forms hydroxide.

Explanation:
1. Sodium reacts violently with water in an exothermic reaction: 2Na + 2H₂O → 2NaOH + H₂.
2. The heat evolved makes the hydrogen catch fire, and the product is sodium hydroxide.

Teacher's Note:
1. The reaction gives out heat, so it is exothermic.
2. The product is a hydroxide, not an oxide.

Answer: (c) 14

Explanation:
1. The second shell holds 8 electrons, so the third shell has 50% of 8, which is 4 electrons.
2. The configuration is 2, 8, 4, so the atomic number is 2 + 8 + 4 = 14.

Teacher's Note:
1. Add the electrons in all shells.
2. The element is silicon, a metalloid.

Answer: (b) Electrical conductivity in solid state

Explanation:
1. Ionic compounds dissolve in water and have high melting and boiling points.
2. In the solid state the ions are held in fixed positions, so they cannot conduct electricity. They conduct only in the molten state or in solution.

Teacher's Note:
1. Conduction needs freely moving ions.
2. Melting or dissolving frees the ions.

Answer: (b) they can share electrons with chlorine

Explanation:
1. Non-metals do not lose electrons easily.
2. They share electrons with chlorine atoms to complete their octets, so they form covalent chlorides.

Teacher's Note:
1. Sharing gives covalent bonds.
2. Metals give electrons, so they form ionic chlorides.

Answer: (b) Sharing of electrons is involved in ionic bonds.

Explanation:
1. An ionic bond is formed by complete transfer of electrons from a metal to a non-metal, not by sharing.
2. The other statements are correct, so (b) is incorrect.

Teacher's Note:
1. Sharing is for covalent bonds.
2. Ionic solids are hard but brittle.

Answer: (d) two

Explanation:
1. The atomic number of calcium is 20 and its configuration is 2, 8, 8, 2.
2. It has 2 valence electrons, which it gives to oxygen.

Teacher's Note:
1. Write the electronic configuration first.
2. Group 2 elements have two valence electrons.

Answer: (d) A is metal and B is non-metal

Explanation:
1. A basic (alkaline) oxide is formed by a metal, so A is a metal.
2. The oxide of B must be acidic to react with the alkali, so B is a non-metal.

Teacher's Note:
1. Alkaline solution comes from a metal oxide.
2. An acid and an alkali react together.

Answer: (b) calcination

Explanation:
1. Calcination is heating a carbonate ore strongly in the absence or limited supply of air to convert it into the oxide.
2. Roasting is done in excess of air for sulphide ores.

Teacher's Note:
1. Calcination: carbonate ore, little or no air.
2. Roasting: sulphide ore, excess air.

Answer: (c) fused sodium chloride

Explanation:
1. In an aqueous solution hydrogen, not sodium, is liberated at the cathode.
2. Sodium is obtained by electrolysis of fused (molten) sodium chloride: sodium is deposited at the cathode and chlorine is released at the anode.

Teacher's Note:
1. Molten salt, not solution, is electrolysed for reactive metals.
2. Cathode: Na+ + e- gives Na.

Answer: (d) All of these

Explanation:
1. Bauxite (Al₂O₃.2H₂O), cuprite (Cu₂O) and haematite (Fe₂O₃) are all oxides of metals.
2. So all of these are oxide ores.

Teacher's Note:
1. Look at the chemical formula of the ore.
2. Oxide ores are the easiest to reduce.

Answer: (b) 2ZnS + 3O₂ → 2ZnO + 2SO₂

Explanation:
1. Roasting is heating a sulphide ore in excess air to get the oxide.
2. Reaction (b) converts zinc sulphide to zinc oxide in air. (a) is calcination, (c) is reduction and (d) is neutralisation.

Teacher's Note:
1. Roasting involves oxygen and a sulphide.
2. Calcination involves a carbonate and no air.

Answer: (a) Fe

Explanation:
1. The oxide used with aluminium in the thermite reaction to join rail tracks is iron(III) oxide.
2. So Z is iron, which lies between Al and Pb and is extracted by carbon reduction.

Teacher's Note:
1. Thermite welding uses Fe2O3 and aluminium.
2. Mg lies above Al and Pb lies below Fe.

Answer: (c) Zinc

Explanation:
1. Galvanisation is coating iron with a thin layer of zinc.
2. Zinc is more reactive than iron, so it protects the iron even if the coating gets scratched.

Teacher's Note:
1. Galvanised iron means zinc-coated iron.
2. Zinc acts as a sacrificial layer.

Answer: (a) 24 carats

Explanation:
1. The purity of gold is expressed in carats.
2. Pure gold is 24 carat, which is too soft for jewellery, so it is alloyed with silver or copper.

Teacher's Note:
1. 22 carat gold is an alloy.
2. Higher carat means purer gold.

Answer: (d) non-metal

Explanation:
1. Graphite is an allotrope of carbon.
2. Carbon is a non-metal, so graphite is a non-metal that conducts electricity.

Teacher's Note:
1. Diamond and graphite are both carbon.
2. Graphite is a good conductor but still a non-metal.

Answer: (a) Copper

Explanation:
1. Copper reacts with oxygen on heating to form black copper(II) oxide: 2Cu + O₂ → 2CuO.
2. Potassium oxide is white, silver does not react and zinc oxide is white/yellowish.

Teacher's Note:
1. Black coating on copper is CuO.
2. Zinc oxide turns yellow when hot and white on cooling.

Answer: (b) C

Explanation:
1. Metal C shows no change in any of the four solutions, not even in silver nitrate.
2. A metal that cannot displace even silver is the least reactive, so C is the least reactive metal.

Teacher's Note:
1. No reaction with any solution means least reactive.
2. Silver is the least reactive metal in the table.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Silver slowly reacts with sulphur compounds in air to form black silver sulphide, so A is true.
2. Silver is indeed a low-reactivity metal, so R is true, but its low reactivity does not explain the tarnishing.

Teacher's Note:
1. Tarnish on silver is silver sulphide.
2. Silver is below hydrogen in the series.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Sodium reacts so vigorously with oxygen and moisture of air that it may catch fire.
2. It is therefore kept in kerosene, in which it does not react, so R explains A.

Teacher's Note:
1. Very reactive metals like Na, K and Li are stored under oil.
2. Kerosene cuts off air and moisture.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Metals have 1 to 3 valence electrons that they lose easily to form positive ions.
2. This tendency to form positive ions is exactly what electropositive means, so R explains A.

Teacher's Note:
1. Electropositive means forms positive ions.
2. Non-metals are electronegative.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Galvanisation means coating iron with zinc.
2. The zinc coating protects iron from rusting, which increases the life of the articles, so R explains A.

Teacher's Note:
1. Zinc coating is a barrier and a sacrificial layer.
2. Galvanised pipes last longer.

Answer: (c) A is true, but R is false.

Explanation:
1. Metals produce a ringing sound when struck, so A is true.
2. Metals are malleable, not brittle. Brittleness is a property of non-metals, so R is false.

Teacher's Note:
1. Metals bend, non-metals break.
2. Sonorous is linked to sound.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Nitric acid is a strong oxidising agent, so it oxidises the hydrogen produced to water.
2. The acid itself is reduced to oxides of nitrogen, so R explains A.

Teacher's Note:
1. Exceptions: Mg and Mn with very dilute HNO3.
2. Nitrogen oxides like NO and NO2 form.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Reactive metals form a hydroxide and hydrogen with water, and less reactive metals form an oxide and hydrogen with steam.
2. The examples of sodium and iron given in R support this statement, so R explains A.

Teacher's Note:
1. Water gives hydroxide, steam gives oxide.
2. In both cases hydrogen is liberated.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. It is easier to obtain a metal from its oxide than from its sulphide or carbonate.
2. That is why sulphide ores are first roasted to oxides, so R explains A.

Teacher's Note:
1. Roast sulphides, calcine carbonates.
2. Then reduce the oxide.