(i) Write the balanced chemical equations when: (I) A mixture of Cu_2O and Cu_2S is heated. (II) ZnS is heated in the presence of oxygen. (ii) Give reasons for the following: (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel. (iii) Show the formation of ionic compound CaO with electron dot structure. [Atomic number: Ca = 20, O = 8] (i) Write the balanced chemical equations when: (I) A mixture of Cu_2O and Cu_2S is heated. (II) ZnS is heated in the presence of oxygen. (ii) Give reasons for the following: (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel. (iii) Show the formation of ionic compound CaO with electron dot structure. [Atomic number: Ca = 20, O = 8]

ScienceCBSE Class 10 · Board exam 2026, set 31/5/1 · 5 marks · Long answer

CBSE Class 10 Science 2026: question 29(B)

Set in the CBSE Class 10 board exam of 2026, paper 31/5/1, section B, question 29(B), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q29(B) · 5 marks · Long answerMetals and Non-metals

(i) Write the balanced chemical equations when:
(I) A mixture of $C u_{2} O$ and $C u_{2} S$ is heated.
(II) ZnS is heated in the presence of oxygen.
(ii) Give reasons for the following:
(I) The wires carrying current in homes have a coating of PVC.
(II) To make hot water tanks, copper is used and not steel.
(iii) Show the formation of ionic compound CaO with electron dot structure. [Atomic number: Ca = 20, O = 8]

(i)
Write the balanced chemical equations when: (I) A mixture of Cu $_{2}$ O and Cu $_{2}$ S is heated. (II) ZnS is heated in the presence of oxygen.
2 marks
(ii)
Give reasons for the following: (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel.
2 marks
(iii)
Show the formation of ionic compound CaO with electron dot structure. [Atomic number: Ca = 20, O = 8]
1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Heating ZnS in air is roasting; heating Cu₂O with Cu₂S is self-reduction — both release SO₂.

Hint 2

Is PVC a conductor or an insulator? Which metal does not rust in hot water?

Hint 3

Write electronic configurations of Ca (20) and O (8) to see how many electrons move.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(i)(I) Self-reduction of copper: $2 C u_{2} O + C u_{2} S Heat 6 Cu (s) + S O_{2} (g)$
1 mark
(i)(II) Roasting of zinc blende: $2 ZnS (s) + 3 O_{2} (g) Heat 2 ZnO (s) + 2 S O_{2} (g)$
1 mark
(ii)(I) PVC is a poor conductor of electricity; the coating insulates current-carrying wires and prevents shocks and short circuits.
1 mark
(ii)(II) Copper does not react with cold water, hot water or steam, so it does not corrode, whereas steel (iron) rusts; copper is also a better conductor of heat.
1 mark
(iii) Ca (2, 8, 8, 2) loses 2 electrons; O (2, 6) gains them:
$Ca : + \cdot \ddot{\cdot\cdot O} \cdot \to C a^{2 +} [: \ddot{\cdot\cdot O} :]^{2 -}$ i.e. $C a^{2 +} O^{2 -}$ (CaO). Show the two electrons transferring by arrows from Ca to O.
1 mark

Answer: (i) 2Cu₂O + Cu₂S → 6Cu + SO₂; 2ZnS + 3O₂ → 2ZnO + 2SO₂. (ii) PVC insulates; copper does not react with water/steam (steel rusts). (iii) Ca transfers 2 electrons to O → Ca²⁺[O]²⁻.

Where the marks are

Balanced equation for Cu₂O + Cu₂S (1 mark)
Balanced roasting equation for ZnS (1 mark)
PVC is an insulator (1 mark)
Copper does not react with water/steam or better heat conductor (1 mark)
Electron-dot formation of Ca²⁺O²⁻ (1 mark)

Revise the chapter

Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)
Topic: Metallurgy: Extraction of Metals from Ores

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 10 Science 2026: question 29(B)

Hints

Step-by-step solution

Revise the chapter

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