Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
How to Use This Page
These are complete NCERT Solutions for CBSE Class 10 Science Chapter 3 — Metals and Non-Metals. Follow these steps for best results:
1. Attempt the question yourself first — write the balanced equation, state the product, and note the observation before checking the answer. 2. Compare with the solution given — focus on the reasoning, not just the final answer. 3. For chemical equations — always balance them and include state symbols where asked. 4. For MCQs — read why each wrong option is wrong; this builds deeper understanding. 5. Use the Key Concepts section as a quick revision tool before tests.
Key Concepts (Quick Recap)
Physical Properties of Metals
- Lustre: Metals have a shiny surface (except freshly cut sodium which turns dull quickly).
- Hardness: Most metals are hard (Fe, Cu, Al), but Na, K, and Li are soft and can be cut with a knife.
- Malleability: Can be beaten into thin sheets. Gold and silver are the most malleable.
- Ductility: Can be drawn into thin wires. Gold is the most ductile metal.
- Conductivity: Good conductors of heat and electricity. Silver is the best conductor of heat; copper is the best practical conductor of electricity. Lead and mercury are poor conductors.
- Sonority: Metals produce a ringing sound when hit — used in bells.
- Melting/boiling points: Generally high, but gallium (Ga) melts at 30 °C and mercury (Hg) is liquid at room temperature.
- Density: Generally high, but lithium is the lightest metal.
Exceptions — Non-metals that Behave like Metals
- Iodine is a non-metal but has a lustrous surface.
- Graphite (carbon allotrope) is a non-metal but conducts electricity.
- Diamond (carbon allotrope) is the hardest natural substance.
Reactivity Series (Memorize This!)
The reactivity series lists metals in order of decreasing reactivity:
| Position | Metal | Symbol | Reactivity Level |
|---|---|---|---|
| 1 | Potassium | K | Most reactive — reacts violently with water |
| 2 | Sodium | Na | Very reactive — stored under kerosene |
| 3 | Calcium | Ca | Reacts readily with water |
| 4 | Magnesium | Mg | Reacts with steam, slowly with cold water |
| 5 | Aluminium | Al | Protected by oxide layer |
| 6 | Zinc | Zn | Reacts with steam and dilute acids |
| 7 | Iron | Fe | Reacts with steam and dilute acids |
| 8 | Lead | Pb | Reacts slowly with dilute acids |
| — | Hydrogen | H | Reference element (non-metal) |
| 9 | Copper | Cu | Does not react with water or dilute HCl |
| 10 | Mercury | Hg | Very low reactivity |
| 11 | Silver | Ag | Does not react with most acids |
| 12 | Gold | Au | Least reactive — found native in nature |
Mnemonic: Kings Never Can Make A Zebra Feed Peas. However Copper Helps Silver Alloys Glow.
A metal higher in the series can displace a metal below it from its salt solution.
Chemical Properties of Metals
Chemical Properties of Non-metals
- Non-metal + O₂ → Acidic oxide (e.g., S + O₂ → SO₂; C + O₂ → CO₂)
- Non-metal + H₂ → Covalent hydride (e.g., H₂ + Cl₂ → 2HCl)
- Non-metals do not displace hydrogen from dilute acids.
Ionic Bonding
- Metals (low electronegativity) lose electrons → form cations.
- Non-metals (high electronegativity) gain electrons → form anions.
- Electrostatic attraction between cations and anions = ionic bond.
- Properties of ionic compounds: high melting/boiling points, soluble in water, conduct electricity in molten/aqueous state, hard and brittle.
Corrosion
- Rusting of iron: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O (hydrated iron oxide)
- Conditions for rusting: Presence of both oxygen and moisture.
- Prevention methods: Painting, greasing/oiling, galvanisation (zinc coating), alloying (stainless steel), electroplating, using anti-rust solutions.
Extraction of Metals from Ores
1. Concentration of ore — remove gangue (impurities) by froth flotation, magnetic separation, or gravity separation. 2. Roasting (for sulphide ores) — heat in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂ 3. Calcination (for carbonate ores) — heat in limited air: ZnCO₃ → ZnO + CO₂ 4. Reduction of metal oxide to metal — using carbon (coke) or highly reactive metal:
5. Refining — electrolytic refining: impure metal (anode), pure metal (cathode), salt solution (electrolyte).
- ZnO + C → Zn + CO
- Fe₂O₃ + 3CO → 2Fe + 3CO₂ (blast furnace)
Intext Questions
Page 40 — Physical Properties
Page 46 — Chemical Properties of Metals
Page 49 — Ionic Bonding
Chapter-End Exercise
Q1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and Cu metal (b) MgCl₂ solution and Al metal (c) FeSO₄ solution and Ag metal (d) AgNO₃ solution and Cu metal
Explanation using the reactivity series:
A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution. The reactivity series order is: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
Let us analyse each option:
- (a) NaCl + Cu: Na is far above Cu in the reactivity series. Cu is less reactive than Na, so Cu cannot displace Na. No reaction.
- (b) MgCl₂ + Al: Al is above Mg in the reactivity series (Al > Mg in the series). However, Al is actually below Mg (the correct series: Mg > Al). So Al cannot displace Mg. No reaction.
- (c) FeSO₄ + Ag: Ag is below Fe in the reactivity series (Fe > Ag). Silver is less reactive than iron, so Ag cannot displace Fe. No reaction.
- (d) AgNO₃ + Cu: Cu is above Ag in the reactivity series (Cu > Ag). Copper is more reactive than silver, so Cu can displace Ag. Displacement reaction occurs.
Equation: Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
Q2. Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) All of the above
Detailed reasoning:
- (a) Applying grease — Grease prevents contact with moisture and oxygen, so it does prevent rusting. However, grease is not suitable for a cooking utensil because it would mix with food and is unhygienic. Also, grease would wash off during cooking and cleaning. Not suitable for a frying pan.
- (b) Applying paint — Paint forms a barrier between iron and moisture/oxygen. However, paint is not safe for cooking surfaces as it contains harmful chemicals. Also, paint peels off at high cooking temperatures and during washing. Not suitable for a frying pan.
- (c) Applying a coating of zinc (galvanisation) — Zinc forms a protective layer that does not peel off easily. Even if the zinc coating gets scratched, zinc (being more reactive than iron) sacrificially corrodes first, protecting the underlying iron. Zinc is safe for food contact. Most suitable method.
- (d) All of the above — Since (a) and (b) are not suitable for a cooking utensil, this option is incorrect for the context of a frying pan.
Q3. 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
The clue is that the oxide formed has a high melting point and is soluble in water.
- (a) Calcium (Ca): Ca + O₂ → CaO (calcium oxide / quicklime). CaO is an ionic compound with a high melting point (2572 °C). It dissolves in water: CaO + H₂O → Ca(OH)₂ (calcium hydroxide). This matches both conditions.
- (b) Carbon (C): C + O₂ → CO₂ (carbon dioxide). CO₂ is a gas at room temperature — it does not have a high melting point. Does not match.
- (c) Silicon (Si): Si + O₂ → SiO₂ (silica). SiO₂ has a high melting point but is insoluble in water. Does not match.
- (d) Iron (Fe): Fe forms Fe₂O₃ or Fe₃O₄. Iron oxides have high melting points but are insoluble in water. Does not match.
Only calcium oxide satisfies both conditions — high melting point and water solubility.
Q4. Food cans are coated with tin and not with zinc because:
(a) Zinc is costlier than tin (b) Zinc has a higher melting point (c) Zinc is more reactive than tin (d) Zinc is less reactive than tin
- Zinc is higher than tin in the reactivity series (Zn > Sn). This means zinc is more reactive.
- If zinc were used to coat food cans, it could react with acidic food substances (like citric acid in fruits, acetic acid in pickles), producing zinc salts that would contaminate the food and make it unsafe for consumption.
- Tin is less reactive and does not react with food acids, making it safe for coating food cans.
- Let us check the wrong options:
- (a) is wrong because zinc is actually cheaper than tin, not costlier.
- (b) is wrong because melting point is irrelevant to food safety.
- (d) is wrong because zinc is more reactive, not less.
Q5. You are given a hammer, a battery, a bulb, wires, and a switch. How could you use these to distinguish between samples of metals and non-metals?
Method 1 — Malleability test using the hammer:
Place the sample on a hard surface and strike it with the hammer.
- If the sample flattens into a sheet → it is malleable → metal.
- If the sample breaks into pieces or shatters → it is brittle → non-metal.
Method 2 — Electrical conductivity test using the circuit:
Connect the sample in a simple circuit: battery → wires → sample → bulb → switch → back to battery.
- Close the switch. If the bulb glows → the sample conducts electricity → metal.
- If the bulb does not glow → the sample does not conduct → non-metal (exception: graphite, a non-metal that conducts electricity).
Both tests together give a reliable identification.
Q6. What are amphoteric oxides? Give two examples.
Amphoteric oxides are metal oxides that exhibit both acidic and basic behaviour. They react with acids to form salt and water (like a base) and also react with bases to form salt and water (like an acid).
Example 1 — Aluminium oxide (Al₂O₃):
Reaction with acid (basic behaviour): Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Reaction with base (acidic behaviour): Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (sodium aluminate)
Example 2 — Zinc oxide (ZnO):
Reaction with acid (basic behaviour): ZnO + 2HCl → ZnCl₂ + H₂O
Reaction with base (acidic behaviour): ZnO + 2NaOH → Na₂ZnO₂ + H₂O (sodium zincate)
Q7. Name two metals that react with dilute acids to produce hydrogen gas. Write the equations.
Q8. In the electrolytic refining of a metal M, what would you take as the anode, cathode, and electrolyte?
| Component | What is taken | Reason |
|---|---|---|
| Anode | Thick block of impure metal M | The impure metal dissolves into the electrolyte during electrolysis, leaving impurities behind as "anode mud" |
| Cathode | Thin strip of pure metal M | Pure metal from the electrolyte deposits onto the cathode |
| Electrolyte | Aqueous solution of a soluble salt of metal M | Carries metal ions from anode to cathode. Example: CuSO₄ solution for refining copper |
Process: When electric current is passed, the impure metal at the anode oxidises and enters the solution as Mⁿ⁺ ions. These ions migrate to the cathode, where they are reduced and deposited as pure metal. Impurities either remain in solution or settle as anode mud.
Q9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it. (a) What will be the action of gas on dry litmus paper? (b) What will be the action of this gas on moist litmus paper?
When sulphur is heated in air, it burns with a blue flame to form sulphur dioxide gas:
S(s) + O₂(g) → SO₂(g)
(a) Action on dry litmus paper: No change. SO₂ is an acidic oxide, but acidic properties require the gas to dissolve in water to form an acid. On dry litmus paper, there is no water to dissolve the gas, so no ionisation occurs and no colour change is observed.
(b) Action on moist litmus paper: Blue litmus turns red. The moisture on the paper allows SO₂ to dissolve and form sulphurous acid:
SO₂ + H₂O → H₂SO₃ (sulphurous acid)
This acid turns blue litmus red, confirming that SO₂ is an acidic oxide.
Q10. State two conditions necessary for rusting of iron. What is the chemical formula of rust?
Two conditions necessary for rusting:
1. Presence of oxygen (from air) — iron must be exposed to oxygen for oxidation to occur. 2. Presence of water or moisture — water acts as a medium for the electrochemical process of rusting. Without moisture, iron does not rust even in the presence of oxygen.
Chemical formula of rust: Fe₂O₃·xH₂O (hydrated iron(III) oxide, where x is variable)
Equation for rusting:
4Fe(s) + 3O₂(g) + xH₂O(l) → 2Fe₂O₃·xH₂O(s)
Rust is a reddish-brown, flaky substance that slowly eats away the iron surface. Unlike the oxide coating on aluminium (which is protective), rust does not form a continuous layer and falls off, exposing fresh iron to further corrosion.
Q11. What type of oxides are formed when non-metals combine with oxygen?
Non-metals combine with oxygen to form acidic oxides (also called non-metal oxides). These oxides dissolve in water to form acids.
Examples:
- Sulphur: S + O₂ → SO₂; SO₂ + H₂O → H₂SO₃ (sulphurous acid)
- Carbon: C + O₂ → CO₂; CO₂ + H₂O → H₂CO₃ (carbonic acid)
- Nitrogen: N₂ + O₂ → 2NO; 2NO + O₂ → 2NO₂; 3NO₂ + H₂O → 2HNO₃ + NO (nitric acid)
- Phosphorus: P₄ + 5O₂ → 2P₂O₅; P₂O₅ + 3H₂O → 2H₃PO₄ (phosphoric acid)
Exceptions — Neutral oxides: Some non-metal oxides like carbon monoxide (CO) and nitric oxide (NO) are neutral oxides — they neither react with acids nor bases and do not form acids with water.
Q12. Give reasons:
(a) Platinum, gold, and silver are used to make jewellery.
These metals lie at the bottom of the reactivity series, meaning they are the least reactive metals. They do not react with oxygen, water, or acids in ordinary conditions. As a result:
- They do not corrode or tarnish, retaining their shine and lustre forever.
- They are highly malleable and ductile, allowing them to be crafted into intricate jewellery designs.
- Their unreactive nature ensures that jewellery does not discolour or degrade over time.
(b) Sodium, potassium, and lithium are stored under oil.
These are highly reactive alkali metals at the top of the reactivity series. If exposed to air:
- They react vigorously with oxygen: 4Na + O₂ → 2Na₂O
- They react violently with moisture: 2Na + 2H₂O → 2NaOH + H₂ (the heat produced can ignite hydrogen)
- They can even react with nitrogen in air
Kerosene oil does not contain water or oxygen, so it acts as a protective barrier between the metal and the atmosphere, preventing any reaction.
(c) Aluminium is a highly reactive metal, yet it is used to make cooking utensils.
Aluminium is high in the reactivity series (above zinc and iron). However, when aluminium is exposed to air, it reacts with oxygen to form a thin, tough, and impervious layer of aluminium oxide (Al₂O₃) on its surface:
4Al + 3O₂ → 2Al₂O₃
This oxide layer:
- Is self-healing — if scratched, new Al₂O₃ forms immediately.
- Is non-reactive and prevents further oxidation or corrosion of the underlying aluminium.
- Is stable at cooking temperatures and does not react with most food substances.
- Makes aluminium safe and durable for cooking utensils.
(d) Carbonate and sulphide ores are usually converted to oxides during the process of extraction of metals.
Metal oxides are easier to reduce to the pure metal than carbonates or sulphides. The conversion happens in two ways:
Calcination (for carbonate ores) — heating in limited air: ZnCO₃(s) → ZnO(s) + CO₂(g) CaCO₃(s) → CaO(s) + CO₂(g)
Roasting (for sulphide ores) — heating in excess air: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g) 2Cu₂S(s) + 3O₂(g) → 2Cu₂O(s) + 2SO₂(g)
After conversion to oxides, reduction is straightforward using carbon (coke) as the reducing agent: ZnO + C → Zn + CO
This is why ores are first converted to oxides before reduction to extract the metal.
Common Mistakes to Avoid
1. Confusing Mg and Al position in the reactivity series. Remember: Mg is above Al (Mg > Al). A common error is to place Al above Mg because Al seems "more reactive" in everyday use. The correct order is K > Na > Ca > Mg > Al > Zn > Fe.
2. Writing "iron reacts with water" without specifying steam. Iron does NOT react with cold water. It only reacts with steam: 3Fe + 4H₂O(steam) → Fe₃O₄ + 4H₂. Always specify "steam" in the equation and explanation.
3. Forgetting that copper does not react with dilute HCl. Many students write Cu + 2HCl → CuCl₂ + H₂. This is wrong. Copper is below hydrogen in the reactivity series and cannot displace hydrogen from dilute HCl. Copper does react with dilute HNO₃, but that is due to the oxidising nature of nitric acid, not displacement.
4. Confusing amphoteric oxides with basic oxides. Not all metal oxides are basic. Al₂O₃ and ZnO are amphoteric — they react with both acids AND bases. Always check: if the question mentions the oxide reacting with NaOH, it is testing amphoteric behaviour.
5. Writing incorrect rust formula. Rust is Fe₂O₃·xH₂O (hydrated iron oxide), NOT FeO, NOT Fe₃O₄, and NOT Fe₂O₃ alone. The "xH₂O" (water of crystallisation) is essential — without moisture, there is no rust.
6. Saying "metals are hard" without exceptions. Always mention exceptions: sodium, potassium, and lithium are soft metals that can be cut with a knife. Mercury is liquid. General statements about metals must include exceptions for full marks.
7. Confusing roasting and calcination. Roasting is for sulphide ores (heated in excess air, SO₂ released). Calcination is for carbonate ores (heated in limited air, CO₂ released). Do not mix them up.
8. Forgetting that non-metals can have metallic properties. Graphite conducts electricity; iodine is lustrous; diamond is extremely hard. Do not assume all non-metals are dull, soft insulators — always state "generally" when describing non-metal properties.
9. Wrong reason for tin coating on food cans. The reason is that zinc is more reactive than tin and would react with food acids. Students often write "zinc is toxic" or "tin is cheaper" — both are wrong. Zinc is cheaper than tin; the real reason is reactivity with food acids.
10. Omitting electron configurations in ionic bond formation. When asked to show ionic bond formation, always write the full electronic configuration (e.g., Na: 2,8,1 and Cl: 2,8,7), show the transfer with electron dot structures, and identify the ions formed (Na⁺: 2,8 and Cl⁻: 2,8,8). Skipping the configuration loses marks.
Exam Checklist
Before your exam, make sure you can tick off every item below:
- [ ] I can write the full reactivity series from memory: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
- [ ] I can list at least 5 exceptions to general metal properties (soft metals: Na, K; liquid metal: Hg; lustrous non-metal: I; conducting non-metal: graphite; hardest non-metal: diamond)
- [ ] I can write balanced equations for metals reacting with oxygen, water (and steam), and dilute acids
- [ ] I can explain displacement reactions using the reactivity series and give two examples
- [ ] I can define amphoteric oxides and write equations for Al₂O₃ or ZnO reacting with both acid and base
- [ ] I can show the formation of NaCl from Na and Cl with electron dot structures and full configurations
- [ ] I can list three properties of ionic compounds (high melting point, water solubility, electrical conductivity in molten/aqueous state) and explain each
- [ ] I can state the two conditions for rusting (oxygen + moisture), write the rust formula (Fe₂O₃·xH₂O), and list four methods of prevention
- [ ] I can explain galvanisation and why zinc protects iron even when the coating is scratched (sacrificial protection)
- [ ] I can distinguish between roasting (sulphide ores, excess air, SO₂ released) and calcination (carbonate ores, limited air, CO₂ released)
- [ ] I can describe electrolytic refining — identify anode (impure metal), cathode (pure metal), and electrolyte (salt solution of the same metal)
- [ ] I can explain why platinum, gold, and silver are used for jewellery (low reactivity, no corrosion)
- [ ] I can explain why aluminium is used for cooking utensils despite being reactive (protective Al₂O₃ layer)
Internal Links
- [Chapter 3 Guide — Metals and Non-Metals](/school/cbse/class/10/science/cbse-metals-and-non-metals)
- [All Class 10 Science Solutions](/school/cbse/class/10/science/solutions)
- [Class 10 Science Subject Guide](/school/cbse/class/10/science)