Selina Concise Solutions for ICSE Class 7 Chemistry Chapter 6 Metals and Non metals

Points to Remember :

1. Knowledge of chemistry plays a vital role in the development of human society and civilization.
Chemistry helps us understand the composition of everything around us and how to create new materials for our needs. It has been the foundation for progress in medicine, engineering, and technology.
Teacher's Tip: Think of chemistry as the "building block" of our modern world.
Exam Tip: Use words like "vital" and "civilization" to emphasize the importance of science in your answers.

2. Metals are known to man from ancient times. Metals are used to make our life comfortable.
Humans discovered metals like copper and gold thousands of years ago to make tools and jewelry. Today, they are essential for everything from building skyscrapers to making kitchen utensils.
Teacher's Tip: Metals have been our "best friends" in construction for ages.
Exam Tip: Mentioning "ancient times" shows you understand the history of material science.

3. Non-metals form another class of elements, e.g. hydrogen, oxygen, carbon, etc. They are used for various purposes.
Non-metals are essential for life, such as the oxygen we breathe and the carbon found in all living things. They have very different properties compared to metals, like being poor conductors.
Teacher's Tip: Remember that life cannot exist without non-metals like Oxygen!
Exam Tip: Always provide examples like Oxygen or Carbon when defining non-metals.

4. Alloys are homogeneous solid mixtures containing two or more metals e.g. steel, brass, bronze.
Alloys are created by melting metals together to make a material that is stronger or more resistant to rust than the original metals. For example, steel is much stronger than pure iron.
Teacher's Tip: An alloy is like a "Super Metal" made by mixing others.
Exam Tip: Define an alloy as a "homogeneous mixture" to get full marks.

5. Common salt, hydrocloric acid, carbohydrates, fats, proteins, vitamins, occur naturally and can also be prepared artificially.
These substances are vital for our bodies and are found in the food we eat every day. Scientists can also create them in laboratories to help people who might have deficiencies.
Teacher's Tip: Your kitchen is basically a chemistry lab full of these substances!
Exam Tip: Remember that these can be both "natural" and "synthetic."

6. Fertilizers are artificially prepared substances, which are necessary for the proper growth of crops.
Fertilizers provide essential nutrients like nitrogen and phosphorus to the soil so plants can grow healthy and fast. This helps farmers produce enough food for everyone in the world.
Teacher's Tip: Think of fertilizers as "vitamins" for plants.
Exam Tip: Mention "crop growth" as the primary purpose of fertilizers.

7. There are a number of man-made materials that are used in our daily life for various purposes, e.g., cement, plaster of pairs, plastics.
Human ingenuity has allowed us to create synthetic materials that are durable, cheap, and versatile. These materials have transformed how we build houses and manufacture everyday items.
Teacher's Tip: Almost everything you touch that isn't wood or metal is likely man-made.
Exam Tip: Use the term "man-made" or "synthetic" interchangeably in your descriptions.

8. Medicines are used to cure diseases.
Chemical compounds are carefully formulated to target germs and help our bodies recover from illnesses. Without these advancements in chemistry, many common diseases would still be very dangerous.
Teacher's Tip: Medicines are chemistry's gift to healthcare.
Exam Tip: Always link medicines to "curing diseases" in your definitions.

9. Solution is a homogenous mixture of solute and solvent.
A solution is formed when one substance dissolves completely into another, like sugar in water. The substance that dissolves is the solute, and the one that does the dissolving is the solvent.
Teacher's Tip: Remember: Solute (Small amount) + Solvent (Large amount) = Solution.
Exam Tip: Use the word "homogenous" to describe the uniform nature of a solution.

10. Soda water is prepared by dissolving carbon dioxide in water under high pressure.
The bubbles you see in soda are actually gas trapped inside the liquid. High pressure is required to force the gas to stay dissolved in the water until you open the bottle.
Teacher's Tip: The "fizz" is just CO_2 escaping!
Exam Tip: Mention "high pressure" as it is a key condition for making soda water.

11. Syrup is a highly concentrated sugar solutions. It contains a specific flaviour.
Syrups are very thick because they contain a large amount of sugar dissolved in a small amount of liquid. They are often used in medicines and cooking to add sweetness and taste.
Teacher's Tip: Syrup is just super-sweet, thick water.
Exam Tip: Define syrup as "highly concentrated" to show its high sugar content.

EXERCISE

Question 1: Name a metal
1. that is most malleable : Pure gold
2. that is brittle : Zinc
3. as precious as gold : Platinum
4. that can be cut with knife : Sodium
5. used in making electric cables : Copper
6. used as a thermometric liquid : Mercury
7. that is the best conductor of electricity : Silver
Answer:
1. Pure gold
2. Zinc
3. Platinum
4. Sodium
5. Copper
6. Mercury
7. Silver
These metals are identified by their unique physical properties, such as being very soft or being excellent at carrying electricity. Each property makes the metal suitable for a specific job in our lives.
Teacher's Tip: For conductivity, remember: Silver is the best, but Copper is what we use in wires because it's cheaper!
Exam Tip: When naming metals with special properties, ensure you specify "Pure" for Gold to distinguish it from alloys.

Question 2: Name a non-metal that is :
1. a good conductor of heat and electricity : Graphite (Carbon)
2. hardest naturally occurring substance : Diamond (Carbon)
3. used to kill germs in water : Chlorine
4. lustrous : Iodine
5. used for filling into electric bulbs : Argon
6. used for cancer therapy : Radon
7. liquid at room temperature : Bromine
Answer:
1. Graphite (Carbon)
2. Diamond (Carbon)
3. Chlorine
4. Iodine
5. Argon
6. Radon
7. Bromine
Non-metals are generally gases or brittle solids, but these specific examples are exceptions with very important uses. For example, Graphite is a non-metal that acts like a metal by conducting electricity.
Teacher's Tip: Non-metals usually don't shine, but Iodine is the "shiny" exception!
Exam Tip: Mentioning both "Graphite" and "Diamond" as forms of Carbon shows deep knowledge.

Question 3: Mention two uses of the following metals and non-metals
 

(a) Iron :
Answer: It is used to make pipes, tanks, railing, etc.
It is used in the construction of power transmission towers.

(b) Aluminium :
Answer: It is used to make electric wires.
It is used to make utensils, cans, window fram’es, etc.

(c) Gold :
Answer: It is used for making ornaments and coins.
It is used in the manufacture of electronic devices like computers, telephones, home appliances, etc.

(d) Oxygen :
Answer: It is used by all living beings for breathing.
It is important for combustion.

(e) Iodine :
Answer: It is used in photographic films in the form of potassium iodide.
It is added to salt to make it iodized salt which is necessary for the growth of human body.
These elements are chosen for their specific roles based on how they react or behave. Metals are mostly used for building and electronics, while non-metals like oxygen are vital for biological life.
Teacher's Tip: Iron is the "builder," and Oxygen is the "breather."
Exam Tip: When asked for "two uses," always label them as (i) and (ii) for clarity.

Question 4: Give reasons :

(a) Magnesium is used in fire works.
Answer: Magnesium is used in fire works because it bums with a dazzling light.

(b) Aluminium is used in making aircrafts.
Answer: Aluminium is used in making aircrafts because it is light and strong. It is mixed with other metals to make it stronger.

(c) Copper is used in making electric cables.
Answer: Copper is ductile and a very good conductor of heat and electricity. This is the reason that copper is used in making electric cables.

(d) Graphite is used in the leads of pencils
Answer: Graphite turns paper black that is why it is used in the leads of pencils.

(e) Impure diamond is used to cut glass
Answer: Impure diamond is used to cut glass becuase it is the hardest substance and can easily exert force required for cutting.

(f) Gold is mixed with copper and nickel.
Answer: Pure gold is a very soft metal. It cannot be moulded into ornaments so it is mixed with copper and nickel so that it becomes harder and bit cheaper also.

(g) Tungsten is used in electric bulbs.
Answer: It is a shiny grey metal, in solid state at room temperature. It can withstand high temperature because it has highest melting point among metals. Hence, it is used in electric bulbs.

Providing reasons involves linking a material's physical property to its practical application. For example, the high melting point of Tungsten is exactly why it doesn't melt inside a hot lightbulb.
Teacher's Tip: "Dazzling light" = Magnesium; "Hardest" = Diamond.
Exam Tip: In "Give reasons" questions, always use the word "because" to directly link the property to the use.

Question 5: Name the metals present in the following alloys
1. Brass - Copper and zinc
2. Bronze - Copper and tin
3. Duralumin - Aluminium and copper
4. Stainless steel - Iron, chromium, nickel
Answer:
1. Copper and zinc
2. Copper and tin
3. Aluminium and copper
4. Iron, chromium, nickel
Alloys combine the best traits of different metals to solve engineering problems. Knowing these combinations helps explain why some metals rust and others do not.
Teacher's Tip: Remember "Brass has Zinc" (the letter 's' in brass sounds like 'z').
Exam Tip: For Stainless Steel, don't forget to mention "Chromium" as it prevents rusting.

Question 6: Give four differences between metals and non-metals with reference to their
(a) Melting point and boiling point,
(b) Conductivity of heat and electricity,
(c) Malleability
(d) Solubility
Answer:
Metals - Non-metals
Melting point and boiling point: Metals have both high high melting point and boiling point. - Non-metals have both low melting and low boiling point.
Conductivity of heat and electricity: They are good conductors of heat and electricity. - Non-metals are bad conductors of heat and electricity.
Malleability: Metals are ususally malleable. - All non-metal are non- malleable.
Solubility: Metals are generally insoluble in water and other organic solvents. - They are both soluble and insoluble
This comparison shows that metals and non-metals are almost opposites in how they behave physically. These differences help us categorize every element we find in nature.
Teacher's Tip: If you know one side of the table, the other side is usually the exact opposite!
Exam Tip: When asked for four differences, ensure you address each specific category mentioned in the question.

Question 7: What are metalloids?
Answer: Metalloids are the elements which show some properties of metals and some properties of non-metals. They all are solids. They are silicon, boron, arsenic, antimony, germanium, tellurium and polonium.
Metalloids act as a "middle ground" between shiny metals and dull non-metals. They are incredibly important in the electronics industry because they can partially conduct electricity.
Teacher's Tip: Metalloids are like "half-metals" sitting on the border of the periodic table.
Exam Tip: List at least three examples like Silicon and Boron to make your definition complete.

Question 8: Give two uses of
Answer:
(a) Silicon :
- Highly pure silicon is used in making microchips for computers, transistors, solar cells, rectifiers and other solid state devices that are used extensively in the electronic and present space age industries.
- It is used in the manufacture of a waterproof material called “silicone”. Silicone is used to make bags, umbrellas, raincoats, etc.
- It is an important substance present in steel, an alloy of carbon.
(b) Antimony :
- Antimony is used in electric industry to make semiconductor devices.
- It is alloyed with lead to improve its hardness and strength and is used in batteries.
- It is also used in printing presses as type metal.
(c) Tungsten :
- It is used in making electrodes.
- It is used in heating elements.
- It is used as filaments in electric bulbs and cathode ray tubes.
(d) Germanium:
- Germanium is used as a semiconductor.
- It is used as a transistor in many electronic applications when mixed with arsenic, gallium, antiomony, etc.
- Germanium is also used to form alloys and as a phosphor in fluorescent lamps
These "specialty" elements have revolutionized modern technology, especially in the field of electronics. Their unique ability to act as semiconductors is what makes our smartphones and computers possible.
Teacher's Tip: Silicon is the "brain" of your computer chip!
Exam Tip: When mentioning Silicon, always distinguish it from "Silicone" (the waterproof material).

OBJECTIVE TYPE QUESTIONS

Question 1: Fill in the blanks :
(a) The most ductile metal is silver.
(b) A metal stored in kerosene oil is sodium.
(c) Tungsten metal is a poor conductor of heat.
(d) Pure gold is a soft metal.
(e) Silicon carbide is the hardest compound known to us.
(f) A non-metal used to purify water is phosphorus.
(g) A metal that gives dazzling effect to crackers when they explode is magnesium.
(h) A chemical compound that makes up the striking heads of match sticks is sulphur.
Answer: [Bolded words above]
These quick facts highlight the "superlatives" of chemistry - the hardest, the most ductile, and the most reactive. Knowing these helps you quickly identify materials based on their unique behavior.
Teacher's Tip: Sodium is so reactive that it "hates" air and water, so it hides in kerosene!
Exam Tip: For fill-in-the-blanks, always use the most specific term provided in your textbook.

Question 2: Match the following :
Column A - Column B
(a) Helium - (1) Electric bulb
(b) Neon - (2) Thermometer
(c) Argon - (3) Semiconductor
(d) Germanium - (4) Weather balloons
(e) Mercury - (5) Advertising signboards

Answer:
(a) Helium - (4) Weather balloons
(b) Neon - (5) Advertising signboards
(c) Argon - (1) Electric bulb
(d) Germanium - (3) Semiconductor
(e) Mercury - (2) Thermometer
This matching exercise helps students associate specific elements with their common industrial or everyday uses. By understanding the properties of these substances, like the non-reactivity of noble gases or the thermal expansion of mercury, we can see why they are chosen for these specific tasks.
Teacher's Tip: Think of 'Neon Lights' for bright city signs and 'Mercury' as the rising silver line in a thermometer when it gets hot.
Exam Tip: In matching questions, always cross out options as you use them to ensure you don't use the same answer twice and to narrow down the remaining choices.

Question 3: Write ‘true’ or ‘false’ for the following statements :

(a) Silver is used to make electric cables :
Answer: False

(b) Iodine acts as an antiseptic in the form of tincture of iodine :
Answer: True

(c) Sodium can be cut with a knife :
Answer: True

(d) Antimony is a metal :
Answer: False

(e) Sand is an oxide of silicon :
Answer: True

This section tests your ability to spot common misconceptions in chemistry. For example, while Silver is the best conductor, it's too expensive for large cables, so we use Copper instead.
Teacher's Tip: Remember, Antimony is a metalloid, not a metal!
Exam Tip: For "False" statements, mentally try to think of the "True" version to help you learn.

MULTIPLE CHOICE QUESTIONS

Question 1: The noble gas used in advertising signboards is
(a) Helium
(b) Neon
(c) Argon
(d) Krypton
Answer: (b) Neon
Neon glows with a distinct reddish-orange light, which is why it has been used for decades in bright city signs. It is a stable gas that doesn't react with the glass tube it is held in.
Teacher's Tip: Just think of the term "Neon Signs."
Exam Tip: Only tick one box for multiple-choice questions unless otherwise told.

Question 2: A metal with melting point less than 50°C is
(a) Gallium
(b) Iron
(c) Gold
(d) Aluminium
Answer: (a) Gallium
Gallium is famous for being a metal that can melt in your hand because its melting point is just 29.7°C. Most other metals require a furnace with temperatures over 1000°C to melt.
Teacher's Tip: Gallium is the "melting metal" trick element.
Exam Tip: Remember that 50°C is relatively low for metals; only Gallium and Mercury fit such categories.

Question 3: A metal which is neither ductile nor malleable is
(a) Copper
(b) Silver
(c) Zinc
(d) Aluminium
Answer: (c) Zinc
While most metals can be hammered into sheets or drawn into wires, Zinc is quite brittle and will shatter if you try to deform it too much. This makes it an exception to the general rule that all metals are malleable.
Teacher's Tip: Zinc is the "stubborn" metal that breaks instead of bending.
Exam Tip: Use Zinc as your go-to example for a "brittle metal."

Question 4: Rust is a hydrated oxide of iron which is
(a) Reddish brown
(b) Green
(c) White
(d) Black
Answer: (a) Reddish brown
Rust occurs when iron reacts with oxygen and moisture in the air. This chemical change produces a flaky coating that eventually eats away at the metal, causing it to weaken.
Teacher's Tip: You've seen rust on old nails or bikes; it's always that orange-brown color.
Exam Tip: Use the full chemical name "hydrated iron oxide" for extra marks.

Question 5: Aluminium is not used to make :
(a) Foils
(b) Wires
(c) Fireworks
(d) Utensils
Answer: (c) Fireworks
Magnesium, not Aluminium, is the primary metal used to create bright flashes in fireworks. Aluminium is great for everyday objects because it is light and doesn't rust easily.
Teacher's Tip: Aluminium is for wrapping sandwiches, not for exploding in the sky!
Exam Tip: Read "NOT used" carefully in the question; it's a common trap.

Question 6: A metalloid used in the manufacture of microchips used in computer is :
(a) Antimony
(b) Germanium
(c) Silicon
(d) Arsenic
Answer: (c) Silicon
Silicon's ability to control the flow of electricity makes it the perfect material for building tiny circuits. This is why the tech hub in California is famously called "Silicon Valley."
Teacher's Tip: Silicon = Computers.
Exam Tip: Silicon is the most widely used semiconductor; always pick it for microchip questions.

Question 7: A metalloid used to make glass :
(a) Sulphur
(b) Germanium
(c) Silicon
(d) Antimony
Answer: (c) Silicon
Ordinary sand is mostly made of silicon dioxide, which is the raw material used to manufacture glass. By heating sand to extremely high temperatures, it turns into the clear glass we use for windows and bottles.
Teacher's Tip: Sand is just the "dust" version of what makes glass.
Exam Tip: Remember that Silicon is found in both computer chips and glass products.

ADDITIONAL QUESTIONS

A. Fill in the blank spaces by choosing the correct words from the given list.
List: amalgam, chlorine, gallium, sodium chloride, silver chloride

1. Gallium is a liquid metal.
2. Salt of silver, such as silver chloride is used for making photographic films.
3. A solution of a metal in mercury is called amalgam.
4. A gas used to sterilisation of drinking water is chlorine.
5. Saline glucose is a solution of glucose and sodium chloride.
Answer: [Bolded words above]
These blanks fill in key industrial and medical uses of chemicals. For example, using chlorine to clean water has saved millions of lives from waterborne diseases.
Teacher's Tip: "Saline" is just the medical word for salty water.
Exam Tip: Cross out words from the list as you use them to avoid repeating choices.

B. Statements given below are incorrect. Write the correct statements :

Question 1: Chlorine gas is used in the manufacture of sulphuric acid.
Answer: Chlorine gas is used in the manufacture of hydrochloric acid.
Chlorine is a key ingredient for making acids that contain chlorine. Sulphuric acid, on the other hand, is made primarily from sulphur and oxygen.
Teacher's Tip: Keep the "Chlor-" names together: Chlorine makes Hydrochloric acid.
Exam Tip: When correcting statements, rewrite the entire sentence clearly.

Question 2: Bronze is a mixture of 10% copper, 80% zinc and 10% tin.
Answer: Bronze is a mixture of 80% copper, 10% zinc and 10% tin.
Bronze is mostly copper, which gives it its reddish-brown color. The other metals are added to make it much harder than pure copper.
Teacher's Tip: Most alloys have one "main" metal that makes up the bulk of the mixture.
Exam Tip: Memorize that Bronze is "Copper-heavy" while Brass is "Copper and Zinc."

Question 3: Soda water is prepared by dissolving washing soda in water.
Answer: Soda water is prepared by dissolving carbon dioxide in water.
Washing soda is for cleaning clothes, but carbon dioxide gas is what gives fizzy drinks their bubbles. Drinking washing soda would be very dangerous!
Teacher's Tip: Don't let the similar names trick you; Soda water needs gas bubbles.
Exam Tip: Mention CO₂ by its full name "Carbon dioxide" for a better score.

Question 4: Aluminium is best conductor of electricity.
Answer: Silver is best conductor of electricity.
Silver allows electrons to flow with the least amount of resistance. However, because silver is so expensive, we usually use copper or aluminium for our home's wiring.
Teacher's Tip: Silver is the "Gold Medalist" of electricity conduction.
Exam Tip: If a question asks for the "best" conductor, the answer is always Silver.

Question 5: Zinc is used for making power transmission wires.
Answer: Copper is used for making power transmission wires.
Copper is used because it combines high conductivity with being flexible and relatively affordable. Zinc is not a good enough conductor for long-distance power lines.
Teacher's Tip: Copper = Electricity.
Exam Tip: Remember that while Silver is best, Copper is the practical choice for most wiring.

C. Match the statements in Column A, with those in Column B.

Column A
1. A metal used for making high quality mirrors.
2. A metal which neither malleable nor ductile.
3. A non-metal used in the sterilisation of water.
4. A non-metal, whose deficiency can lead to disease like goitre.
5. A non-metal which can be used as dry lubricant.

Column B
(a) Chlorine
(b) Graphite
(c) Iodine
(d) Silver
(e) Zinc

Answer:
1. A metal used for making high quality mirrors. - (d) Silver
2. A metal which neither malleable nor ductile. - (e) Zinc
3. A non-metal used in the sterilisation of water. - (a) Chlorine
4. A non-metal, whose deficiency can lead to disease like goitre. - (c) Iodine
5. A non-metal which can be used as dry lubricant. - (b) Graphite
These matching pairs connect chemical elements to their specialized functions in technology and health. For example, the slipperiness of graphite makes it a perfect dry lubricant, while chlorine's ability to kill germs makes it essential for cleaning water.
Teacher's Tip: Use "Silver shines" for mirrors and "Chlorine cleans" for water sterilization to remember these quickly.
Exam Tip: Always write the full correct pair (Statement - Answer) rather than just drawing lines to ensure the examiner gives you full marks for clarity.

D. Write ‘True’ or ‘False’ in front of following statements.
Question 1: Stainless steel is used for making power transmission wires.
Answer: False. Copper is used for making power transmission wires.
Stainless steel is too heavy and not a good enough conductor for wires. Its main job is to be strong and rust-free in the kitchen or hospital.
Teacher's Tip: Steel is for strength, Copper is for power.
Exam Tip: Always check if the material's property matches the use (e.g., strength vs. conductivity).

Question 2: Brass is an alloy of copper and zinc and has lustrous yellow colour.
Answer: True.
Brass looks a lot like gold because of its bright yellow shine, which is why it's often used for decorative items like doorknobs and musical instruments. It is much cheaper and harder than real gold.
Teacher's Tip: Brass looks "Bold" and "Gold."
Exam Tip: Remember the two metals in Brass are Copper and Zinc.

Question 3: Graphite is used in making filaments of electric bulb.
Answer: False. Tungsten is used in making filaments of electric bulb.
Graphite would simply burn up or crumble if used as a filament. Tungsten is unique because it can get white-hot without melting, allowing it to produce light for a long time.
Teacher's Tip: Only Tungsten has the "heat-resistance" for old-school lightbulbs.
Exam Tip: "Filament" is a keyword that should immediately make you think of "Tungsten."

Question 4: Magnesium is used in making light weight alloys of aluminium.
Answer: True.
Magnesium is even lighter than aluminium, so mixing them creates an alloy that is both incredibly light and very strong. This is perfect for building things that need to fly, like airplanes.
Teacher's Tip: Magnalium (Magnesium + Aluminium) is the "Aviation Alloy."
Exam Tip: Remember that Magnesium is a "lightweight champion" metal.

Question 5: Non-metals are poor conductors of electricity.
Answer: True.
Unlike metals, the electrons in most non-metals are not free to move around, so electricity cannot pass through them. This is why we use non-metals like plastic or rubber to coat our electric wires for safety.
Teacher's Tip: Non-metals are "Insulators."
Exam Tip: Always mention "Graphite" as the one exception if you are describing non-metal conductivity.

E. Tick (√) the most appropriate answer.

1. Copper metal is used in :
(a) making electric wires
(b) filling tooth cavities
(c) making fuse wires
(d) preparation of hydrogen
Answer: (a)
Copper's excellent conductivity and flexibility make it the standard material for electrical wiring worldwide. Most of the wires in your house are made of high-quality copper.
Teacher's Tip: Copper is the "Electrician's Metal."
Exam Tip: Copper is the correct answer for "practical" wiring; Silver is for "best" conduction.

2. Sodium amalgam is prepared by dissolving sodium in :
(a) molten copper
(b) dilute vinegar
(c) mercury
(d) molten silver
Answer: (c)
An amalgam is by definition any alloy that contains mercury. Because mercury is a liquid at room temperature, it can dissolve other metals like sodium to form a semi-solid mixture.
Teacher's Tip: Any time you see "Amalgam," think "Mercury"!
Exam Tip: Memorize the term "Sodium Amalgam" as a specific example of a mercury solution.

3. Bronze is an alloy of :
(a) copper and tin
(b) copper and zinc
(c) tin and zinc
(d) copper, zinc and tin
Answer: (a)
Bronze was one of the first alloys ever made by humans, marking the transition from the Stone Age to the Bronze Age. It is harder than copper and lasts a very long time without decaying.
Teacher's Tip: Bronze has 'n' in it, so it contains Ti'n'.
Exam Tip: Don't confuse Bronze (Tin) with Brass (Zinc).

4. Graphite is used :
(a) for sterilisation of water
(b) for making stainless steel
(c) as dry lubricant
(d) in making electric bulbs
Answer: (c)
The layers of atoms in graphite can slide over each other very easily, which is why it feels slippery. This makes it a great lubricant for machines that run at high temperatures where oil might evaporate.
Teacher's Tip: Graphite is like "Slippery Carbon."
Exam Tip: Remember that "pencil lead" is actually graphite, which is why it slides across paper so smoothly.

5. A metal which is a poor conductor of electricity is :
(a) zinc
(b) aluminium
(c) tungsten
(d) iron
Answer: (c)
While all metals conduct electricity, Tungsten has much higher resistance than metals like copper. This resistance is actually useful because it causes the metal to heat up and glow brightly in lightbulbs.
Teacher's Tip: High resistance = Glowing hot.
Exam Tip: Poor conductor among metals usually refers to Tungsten or Bismuth.

STUDY QUESTIONS

1. (a) What do you understand by the term metal?
Answer: The elements which are generally hard solids, have lusture, are malleable and ductile and good conductors of heat and electricity are called metals.
Metals form the largest group of elements in the periodic table and are found on the left side. Their "metallic" properties come from the way their atoms share electrons freely.
Teacher's Tip: If it shines and bends without breaking, it's probably a metal!
Exam Tip: List at least three properties (like lusture, malleable, conductor) to make a perfect definition.

(b) State any five physical properties of a metal.
Answer: Physical properties of a metal :
1. State : Metals are generally solid at room temperature. Mercury and gallium are liquid metals.
2. Hardness : Metals are generally hard.
3. Conductivity : Metals in general are good conductors of heat and electricity. Bismuth and tungsten are exceptions.
4. Malleability : The property by which metals can be beaten into sheets is called malleability. Metals are generally malleable.
5. Ductility : Metals are generally ductile i.e., can be drawn into wires.
These properties define how we use metals in our daily life, such as using copper for wires because it is ductile. Exceptions like Mercury being liquid are just as important to remember.
Teacher's Tip: Use the acronym "MS-HCD" (Malleable, Solid, Hard, Conductive, Ductile).
Exam Tip: Number your points 1 to 5 to show you've met the question's requirement exactly.

2.
(a) Name one metal which is a liquid at room temperature :
Answer: Mercury

(b) Name a metal which can be cut with a knife :
Answer: Sodium

(c) Name a metal which is lighter than water :
Answer: Sodium

(d) Name a metal which is not malleable :
Answer: Zinc

(e) Name a metal which is best conductor of electricity :
Answer: Silver

(f) Name a metal which is poor conductor of electricity :
Answer: Tungsten

These examples show that metals can have very surprising properties that break the "normal" rules. Sodium is so soft it's like wax, and Mercury is the only metal you can pour like water.
Teacher's Tip: These are the "Exceptions to the Rules" list.
Exam Tip: These are very popular one-mark questions; memorize this list perfectly!

3. State two important uses of following metals :
Answer: 
(a) Uses of gold :
- It is used for making jewellery and coins.
- It is used in dentistry for filling cavities in teeth

(b) Uses of silver :
- It is used for making coins and ornaments.
- It is used for making high quality glass mirrors.

(c) Uses of copper :
- It is used for making electric transmission wires.
- It is used for making utensils.

(d) Uses of iron :
- It is used in the construction of buildings.
- It is used in the construction of automobiles, railway bridges and many kinds of machines.

(e) Uses of tin :
- It is used for tinning food cans and the cooking vessels made from copper or iron.
- It is used for making alloys, such as brass and bronze.

(f) Uses of zinc :
- It is used for galvanizing iron sheets to prevent iron from rusting.
- It is used for making alloys such as brass and bronze.

(g) Uses of aluminium :
- Aluminium foils are used for packing food stuff, medicines etc.
- It is used for making high voltage electric transmission wires.

(h) Uses of lead :
- It is used for making lead acid batteries used in all kinds of automobiles.
- It is used for making sanitary pipes.

(i) Uses of magnesium :
- It bums with dazzling white flame and hence is used in fire works.
- It is used in the making of alloys, such as magnalium. This alloy is used in making frame of aeroplanes.

(j) Uses of mercury :
- It is used as a thermometric liquid in laboratory as well as clinical thermometers.
- Gold amalgam and silver amalgam are used in dentistry for filling tooth cavities.

Each metal's role is chosen based on what it does best, like Mercury's expansion in thermometers or Aluminium's light weight for foils. We use different metals for cooking, medicine, construction, and electronics every single day.
Teacher's Tip: "Galvanizing" is just a fancy word for coating iron with Zinc to stop rust.
Exam Tip: Try to remember one "common" use and one "scientific" use for each metal to provide a balanced answer.

4. (a) What do you understand by the term non-metal?
Answer: The elements which are either gases or soft solids, have no lustre, are non malleable and non-ductile and bad conductors of heat and electricity are called non-metals.
Non-metals are generally the exact opposite of metals in their appearance and behavior. They make up most of our atmosphere and the organic molecules inside our bodies.
Teacher's Tip: Non-metals are the "opposites" of metals.
Exam Tip: Use the prefix "non-" (like non-malleable) to define their properties effectively.

(b) State any five physical properties of a non-metal.
Answer: Physical properties of a non-metal :
1. State : Non-metals are generally gases at room temperature.
2. Hardness : Non-metals are not hard (being gases). In case of solid non-metals, they are hard but brittle in nature.
3. Conductivity : Non-metals are poor conductors of heat and electricity except graphite.
4. Malleability : Non-metals are non-malleable, i.e., they cannot be drawn into sheets.
5. Ductility: Non-metals are non-ductile, i.e., cannot be drawn into wires.
These properties explain why we don't use non-metals for construction; they would break or crumble under pressure. However, these same traits make them great as insulators for safety.
Teacher's Tip: Brittle means "breaks like glass" when hit with a hammer.
Exam Tip: Always mention Graphite as the exception for conductivity in non-metals.

5. (a) Name the non-metal and its natural form, which is the hardest substance.
Answer: Diamond is a form of carbon which is the hardest substance.
Diamond's extreme hardness comes from its unique crystal structure where every carbon atom is strongly bonded to four others. This makes it impossible to scratch with almost any other material.
Teacher's Tip: Diamond is just Carbon that spent a lot of time under high pressure!
Exam Tip: Name both the element (Carbon) and the form (Diamond).

(b) Name a non-metal which is liquid form at room temperature.
Answer: Bromine is liquid at room temperature.
Bromine is a dark reddish-brown liquid that gives off strong, unpleasant-smelling vapors. It is very reactive and rarely found alone in nature.
Teacher's Tip: Bromine is the "liquid cousin" of Chlorine gas.
Exam Tip: Mercury is the liquid metal, Bromine is the liquid non-metal. Don't swap them!

(c) Name a non-metal which is good conductor of electricity.
Answer: Graphite (form of carbon).
Graphite conducts electricity because it has "free" electrons that can move between its layers. This is a very rare property for a non-metal to have.
Teacher's Tip: Your pencil lead is actually an electrical conductor!
Exam Tip: Specify that it is a "form of carbon."

(d) Name a gaseous non-metal, having greenish yellow colour.
Answer: Chlorine.
Chlorine is a very reactive gas that is famous for its use in swimming pools to kill bacteria. It has a very sharp, suffocating smell that is easy to identify.
Teacher's Tip: "Green-ish" starts with 'C' like Chlorine.
Exam Tip: Mention its color whenever you are describing the properties of Chlorine gas.

(e) Name a non-metal whose compounds help in the growth of plants.
Answer: Nitrogen.
Nitrogen is a major component of plant proteins and chlorophyll, which is why farmers use nitrogen-rich fertilizers. Without it, plants would turn yellow and stop growing.
Teacher's Tip: Nitrogen is "Plant Food."
Exam Tip: While Phosphorus also helps, Nitrogen is the primary element linked to leafy green growth.

6. State two important uses of following non-metals
Answer: 
(a) Uses of nitrogen :
- It dilutes the activity of oxygen.
- The compounds of nitrogen are of vital importance to plant for growth.

(b) Uses of oxygen :
- It is essential for respiration in plants and animals.
- It is essential for combustion of fuels.

(c) Uses of chlorine :
- It is used for bleaching cotton and jute fabrics.
- It is used in the sterilization of drinking water.

(d) Uses of iodine :
- Tincture of iodine is used for dressing wounds.
- Small quantities of iodine as sodium iodide or potassium iodide are extremely essential for the proper functioning of human body. It is used in the form of iodized salt.

(e) Uses of graphite :
- Graphite is used as pencil lead.
- It is used as a dry lubricant because it is extremely soft and does not bum even at high temperature.
Non-metals play a critical role in both biology and industry. From the iodine that keeps us healthy to the chlorine that keeps our water safe, these elements are essential parts of modern life.
Teacher's Tip: Oxygen is for breathing, Nitrogen is for growing, Chlorine is for cleaning.
Exam Tip: Ensure you understand the difference between "respiration" (breathing) and "combustion" (burning).

7. (a) What are noble gases? Name all in the order of their increasing density.
Answer: A group of gases which do not react chemically with any other substance are called noble gases. They are helium, neon, argon, krypton, xenon and radon.
Noble gases are found in the last group of the periodic table and are very stable because their electron shells are completely full. They are often called "inert" because they prefer to stay alone.
Teacher's Tip: Think of them as "Nobility" who don't like to mix with the "commoner" elements.
Exam Tip: List them in the correct order: He, Ne, Ar, Kr, Xe, Rn.

(b) State one use each of
- Use of helium : Helium is used for filling weather observation balloons.
- Use of argon : It is used for filling electric bulbs.
Helium is much lighter than air, which allows it to lift balloons into the high atmosphere. Argon is used in lightbulbs because it is non-reactive and won't let the filament burn up.
Teacher's Tip: Helium lifts things; Argon protects things.
Exam Tip: For Helium, specifically mention "weather" or "meteorological" balloons for a more precise answer.

8. (a) What is an alloy?
Answer: A homogeneous mixture of two or more molten metals (or a non-metal) is called an alloy.
(b) Why are alloys made?
 

Answer: Pure metals generally do not have all the properties of a good metal, such as malleability, ductility, tensile strength, hardness, resistance to corrosion etc. Hence, alloys are made to enhance these properties. An alloy will have a better quality than the individual metals (or a non-metal) that form it.
By mixing elements, we can create custom materials for specific needs, such as a metal that is very light but also very strong. This technology allows us to build everything from durable bridges to rust-proof spoons.
Teacher's Tip: An alloy is a "Metal Upgrade."
Exam Tip: Use the word "enhance" to explain why we mix different elements together.

9. State the composition and two uses of following alloys :
Answer: 
(a) Stainless steel: It is an alloy of 83% iron, 1% carbon, 15% chromium and 1% nickel.
Uses of stainless steel :
- It is used for making household utensils.
- It is used for making surgical instruments.

(b) Duralumin : It is an alloy of 95% aluminium, 4% copper, 0.5% manganese and 0.5% magnesium.
Uses of duralumin :
- It is used for making aircraft frames.
- It is used for making household articles.

(c) Brass : It is an alloy of 40% to 20% zinc and 60% to 80% copper.
Uses of brass :
- It is used for making tap and electric switches,
- It is used for making household utensils.

(d) Bronze : It is an alloy of 80% copper, 10% zinc and 10% tin.
Uses of bronze :
- It is used for making statues.
- It is used for making household utensils.
Knowing the "recipe" or composition of these alloys tells us why they are used for specific things. For example, the chromium in stainless steel makes it perfect for surgical tools that must never rust.
Teacher's Tip: Duralumin is the "Flying Alloy" because of its aluminium base.
Exam Tip: If you can't remember the exact percentages, just naming the constituent metals is often enough for partial marks.

10. What is an amalgam? How does an amalgam different from an alloy?
Answer: An amalgam is a homogeneous mixture of a metal in mercury whereas an alloy is a homogeneous mixture of two or more molten metals (or a non-metal) generally made for improving one or more properties of metals.
Example: When sodium dissolves in mercury, it forms sodium amalgam.
When zinc and copper are combined, alloy named brass is formed.
An amalgam is just a specialized sub-type of alloy where one of the ingredients must be Mercury. Because Mercury is a liquid, amalgams are often soft or paste-like before they harden.
Teacher's Tip: Remember: Every amalgam is an alloy, but not every alloy is an amalgam!
Exam Tip: Use the mercury example (Sodium Amalgam) to illustrate your answer clearly.