Which of the following equations represent redox reactions and what are the values for 'p' and 'q' in these equations? Equation 1: Fe_2O_3(s) + 2Al(s) → Al_2O_3(s) + p Fe(l) + heat Equation 2: 2C_4H10(g) + 13O_2(g) △ 8CO_2(g) + q H_2O(g) (A) Only equation 1 is a redox reaction, p = 1 and q = 3 (B) Both equations 1 and 2 are redox reactions, p = 2 and q = 4 (C) Only equation 2 is a redox reaction, p = 2 and q = 10 (D) Both equations 1 and 2 are redox reactions, p = 2 and q = 10

ScienceCBSE Class 10 · Sample paper, session 2025-26 · 1 mark · MCQ

CBSE Class 10 Science sample paper 2025-26: question 17

From the official CBSE sample question paper for 2025-26, section B, question 17, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q17 · 1 mark · MCQChemical Reactions and Equations

Which of the following equations represent redox reactions and what are the values for 'p' and 'q' in these equations?
Equation 1: $F e_{2} O_{3} (s) + 2Al (s) \to A l_{2} O_{3} (s) + p Fe (l) + heat$
Equation 2: $2 C_{4} H_{10} (g) + 13 O_{2} (g) △ 8C O_{2} (g) + q H_{2} O (g)$

(A)Only equation 1 is a redox reaction, p = 1 and q = 3
(B)Both equations 1 and 2 are redox reactions, p = 2 and q = 4
(C)Only equation 2 is a redox reaction, p = 2 and q = 10
(D)Both equations 1 and 2 are redox reactions, p = 2 and q = 10

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Count Fe atoms on each side of equation 1, and H atoms on each side of equation 2.

Hint 2

In each reaction, which substance gains oxygen and which loses it?

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.

Equation 1: the left side has 2 Fe in Fe $_{2}$ O $_{3}$ , so the right side needs 2Fe, giving p = 2. Fe $_{2}$ O $_{3}$ loses oxygen (reduced) and Al gains oxygen (oxidised), so it is redox.
Equation 2: the left side has $2 \times 10 = 20$ H atoms, so 10H $_{2}$ O is needed, giving q = 10. Check O: $13 \times 2 = 26$ on the left and $16 + 10 = 26$ on the right. Butane is oxidised and O $_{2}$ is reduced, so it is redox.
Both are redox reactions, with p = 2 and q = 10: option (D).
1 mark

Answer: Option (D): both redox, p = 2, q = 10

Where the marks are

Balances to get p = 2 and q = 10 and identifies both as redox, option (D) (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 2025-26: every question, by section.

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CBSE Class 10 Science sample paper 2025-26: question 17

Hints

Step-by-step solution

Revise the chapter

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