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Answer the following. (Class 10 Science 2025, Q27a)

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

CBSE Class 10 Science 2025: question 27(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/2/1, section C, question 27(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27(a) · 3 marks · Short answerChemical Reactions and Equations

Answer the following.

  1. (i)

    Define the term decomposition reaction. Write one chemical equation each for decomposition reaction where energy is supplied in the form of heat, light or electricity.

    0 marks
  2. (ii)

    Decomposition of vegetable matter into compost is considered an exothermic reaction. Why?

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/2/1.

Hints

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

Hint 1

Decomposition means 'breaking down'. How many reactants does it start with?

Hint 2

Recall heating limestone, silver chloride in sunlight, and electrolysis of water. For (ii), does a compost heap feel warm or cold?

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. (i) Decomposition reaction: a reaction in which a single reactant breaks down to form two or more simpler products.

    ½ mark

  2. Heat (thermal decomposition):

    ½ mark

  3. Light (photolytic decomposition):

    ½ mark

  4. Electricity (electrolytic decomposition):

    ½ mark

  5. (ii) When vegetable matter decomposes into compost, heat (energy) is released. A compost pit becomes warm. A reaction that releases heat is exothermic.

    1 mark

Answer: (i) Single reactant → two or more products; e.g. CaCO₃ → CaO + CO₂ (heat), 2AgCl → 2Ag + Cl₂ (light), 2H₂O → 2H₂ + O₂ (electricity). (ii) Heat is released during decomposition.

Where the marks are

  • Correct definition of decomposition reaction (½ mark)
  • Balanced equation using heat (½ mark)
  • Balanced equation using light (½ mark)
  • Balanced equation using electricity (½ mark)
  • Reason: energy/heat is released, so exothermic (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 31/2/1: 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.