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For Questions number 17 to 20… (Science 2025 31/1/1 Q17)

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ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 1 mark · Assertion-reason

CBSE Class 10 Science 2025: question 17

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section A, question 17, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q17 · 1 mark · Assertion-reasonCompetency-basedChemical Reactions and Equations

For Questions number 17 to 20, two statements are given, one labelled as Assertion (A) and the other labelled as Reason (R).
Assertion (A): Decomposition reactions are generally endothermic reactions.
Reason (R): Decomposition of organic matter into compost is an exothermic process.

  1. (A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  2. (B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  3. (C)Assertion (A) is true, but Reason (R) is false.
  4. (D)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/1/1.

Hints

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

Hint 1

Check each statement on its own first.

Hint 2

Does an exothermic example explain why most decompositions are endothermic?

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.

  1. Assertion: Decomposition reactions need energy (heat, light or electricity) to break bonds, so they are generally endothermic. The Assertion is true.

  2. Reason: Composting releases heat, so it is exothermic. The Reason is true.

  3. The Reason is an exception and does not explain why decomposition is generally endothermic. The answer is option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Chooses option (B) (1 mark)

Revise the chapter

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 paper2025 board paper, set 31/1/1: 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.