Class 10 Science – Chapter: Metals and Non-Metals

NCERT Intext Questions + Back Exercise Answers

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🔹 Intext Questions (Page 40–41)

Q1. Give an example of a metal which
(a) is a liquid at room temperature
(b) can be easily cut with a knife
(c) is the best conductor of heat
(d) is a poor conductor of heat
Answer:
(a) Mercury (Hg)
(b) Sodium (Na) / Potassium (K)
(c) Silver (Ag)
(d) Lead (Pb)

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Q2. Explain the meanings of malleable and ductile.
Answer:

• Malleable → Metals can be hammered into thin sheets (e.g. gold, silver).

• Ductile → Metals can be drawn into thin wires (e.g. copper, aluminium).

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🔹 Intext Questions (Page 46)

Q1. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium reacts vigorously with oxygen and water, producing heat and hydrogen gas. To prevent accidental reaction, it is stored under kerosene oil.

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Q2. Write equations for the reactions of:
(i) Iron with steam
(ii) Calcium and potassium with water
Answer:
(i) 3Fe + 4H₂O (steam) → Fe₃O₄ + 4H₂ ↑
(ii) Ca + 2H₂O → Ca(OH)₂ + H₂ ↑
K + H₂O → KOH + H₂ ↑ + Heat (very vigorous reaction)

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Q3. Samples of four metals A, B, C and D were taken and added to the following solutions: CuSO₄, ZnSO₄, FeSO₄, and AgNO₃. The results are:

• A displaces B, C and D from solutions.

• B displaces C and D from solutions.

• C displaces D from solution.

• D does not displace any metal.

Arrange A, B, C, D in order of decreasing reactivity.
Answer:
Reactivity order: A > B > C > D

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🔹 Intext Questions (Page 49)

Q1. Which gas is produced when a metal reacts with dilute HCl? How will you test for its presence?
Answer:

• Hydrogen gas (H₂) is produced.

• Test: Bring a burning matchstick near the gas; it burns with a pop sound.

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Q2. Iron articles are coated with zinc. Why?
Answer:
To prevent rusting. This process is called galvanisation. Zinc protects iron from moisture and oxygen.

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🔹 Intext Questions (Page 53)

Q1. Explain the following:
(a) Sodium, potassium and calcium are stored under oil.
(b) Aluminium is a highly reactive metal but does not corrode easily.
(c) Copper does not displace hydrogen from acids, but reacts with oxygen.
(d) Metals like Na, K, Ca never occur in free state.
Answer:
(a) They react vigorously with air/water, so stored under oil.
(b) A protective thin oxide layer prevents corrosion.
(c) Copper is less reactive than hydrogen, so cannot displace it, but reacts with oxygen on heating.
(d) They are highly reactive, hence occur only in combined state.

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🔹 Intext Questions (Page 55)

Q1. Metallic oxides of zinc, magnesium and copper were heated with the following metals:

Metal	ZnO	MgO	CuO
Zn	No reaction	No reaction	Zn + CuO → ZnO + Cu
Mg	Mg + ZnO → MgO + Zn	No reaction	Mg + CuO → MgO + Cu
Cu	No reaction	No reaction	No reaction

Q11. Explain why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:

• Copper does not react with cold or hot water, and resists corrosion.

• Steel (iron) reacts with water and corrodes (forms rust).

• Therefore, copper is preferred for making hot water tanks.

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Q12. Give reasons:
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Answer:
(a) They are lustrous, malleable, ductile, resistant to corrosion.
(b) They react vigorously with oxygen/water, hence kept under oil.
(c) Aluminium forms a thin protective oxide layer, making it resistant to corrosion.
(d) It is easier to reduce oxides to metals than carbonates/sulphides.

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Q13. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. State whether the element is a metal or a non-metal.
Answer:

• The compound with oxygen is likely a basic oxide (high melting point, soluble in water forming alkali).

• Hence, the element is a metal.