ScienceCBSE Class 10 · Sample paper, session 2026-27 · 5 marks · Long answer

CBSE Class 10 Science sample paper 2026-27: question 29(A)

From the official CBSE sample question paper for 2026-27, section B, question 29(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q29(A) · 5 marks · Long answerCompetency-basedChemical Reactions and Equations

Attempt either option A or B. A. I. Refer to the dialogue between Alisha, Drishti and Bhushan in the chemistry lab. They are discussing rusting of iron and formation of ammonia gas. Who all do you agree with and why? Alisha: The formation of ammonia by reaction of nitrogen with hydrogen is a reduction reaction. Dristhti: Both rusting of iron and formation of ammonia are redox reactions. Bhushan: Rusting of iron is an oxidation reaction. II. Assess the following chemical equations. Identify the error(s) and rewrite the equation after correction. (i) $MgC l_{2} + AgN O_{3} \to AgC l_{2} + MgN O_{3}$ (ii) $Al + H_{2} S O_{4} \to A l_{2} S O_{4} + H_{2} O$

I
Refer to the dialogue between Alisha, Drishti and Bhushan in the chemistry lab. Who all do you agree with and why?
0 marks
II
Assess the following chemical equations. Identify the error(s) and rewrite the equation after correction. (i) $MgC l_{2} + AgN O_{3} \to AgC l_{2} + MgN O_{3}$ (ii) $Al + H_{2} S O_{4} \to A l_{2} S O_{4} + H_{2} O$
0 marks

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Can one substance be oxidised without another being reduced?

Hint 2

In each reaction, identify which substance gains hydrogen or oxygen and which one loses it.

Hint 3

For II, check the valencies of Ag, Mg and Al, and recall which gas a metal gives with a dilute acid.

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 agree fully with Drishti. Alisha and Bhushan are only partially correct, because oxidation and reduction always occur together (redox).
1 mark
In $N_{2} + 3 H_{2} \to 2N H_{3}$ , nitrogen gains hydrogen and is reduced, while hydrogen is oxidised. So ammonia formation is redox, not just reduction (Alisha saw only half of it).
In rusting, $4Fe + 3 O_{2} + x H_{2} O \to 2F e_{2} O_{3} \cdot x H_{2} O$ , iron gains oxygen and is oxidised, while oxygen is reduced. So rusting is also redox, not just oxidation (Bhushan saw only half of it).
2 marks
II (i). Errors: silver has valency 1, so the product is AgCl, not $AgC l_{2}$ . Magnesium has valency 2, so the nitrate is $Mg (N O_{3})_{2}$ , not $MgN O_{3}$ . The equation must then be balanced.
Corrected: $MgC l_{2} + 2AgN O_{3} \to 2AgCl + Mg (N O_{3})_{2}$
1 mark
II (ii). Errors: aluminium has valency 3 and sulphate has valency 2, so the salt is $A l_{2} (S O_{4})_{3}$ , not $A l_{2} S O_{4}$ . A metal reacting with a dilute acid gives hydrogen gas, not water. The equation must also be balanced.
Corrected: $2Al + 3 H_{2} S O_{4} \to A l_{2} (S O_{4})_{3} + 3 H_{2}$
1 mark

Answer: I. Drishti (Alisha and Bhushan are partly correct), as both reactions are redox. II. (i) $MgC l_{2} + 2AgN O_{3} \to 2AgCl + Mg (N O_{3})_{2}$ ; (ii) $2Al + 3 H_{2} S O_{4} \to A l_{2} (S O_{4})_{3} + 3 H_{2}$

Where the marks are

Agrees with Drishti, noting that Alisha and Bhushan are partially correct (1 mark)
Explains that oxidation and reduction occur together, naming the species oxidised and reduced in both reactions (2 marks)
Corrected and balanced equation (i) (1 mark)
Corrected and balanced equation (ii) (1 mark)

Revise the chapter

Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)
Topic: Balancing Chemical Equations

Practise this chapterBoard-style questions from Chemical Reactions and Equations, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: every question, by section.

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CBSE Class 10 Science sample paper 2026-27: question 29(A)

Hints

Step-by-step solution

Revise the chapter

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