Skip to content

List the possible sources of… (Class 10 Science 2025, Q21a)

questionbuddy.in/q/cbse-10-science-2025-31-3-1-q21a-list-possible-sources-energy-required

ScienceCBSE Class 10 · Board exam 2025, set 31/3/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 21(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/3/1, section B, question 21(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21(a) · 2 marks · Very short answerChemical Reactions and Equations

List the possible sources of energy required in decomposition reactions. Illustrate any one with a suitable example.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/3/1.

Hints

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

Hint 1

Think of the three forms of energy that can break a compound apart.

Hint 2

Recall the reaction used in black-and-white photography.

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. Decomposition reactions need energy from heat (thermal decomposition), light (photolytic decomposition) or electricity (electrolytic decomposition).

    1 mark

  2. Example (light): silver bromide decomposes in sunlight into silver and bromine, which is why it is used in black-and-white photography: .

    1 mark

Answer: Heat, light, electricity; e.g.

Where the marks are

  • Lists heat, light and electricity as energy sources (1 mark)
  • Gives one correct example with balanced equation (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 31/3/1: 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.