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Why do we balance a chemical… (Class 10 Science 2025, Q27A)

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ScienceCBSE Class 10 · Board exam 2025, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2025: question 27(A)

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, 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

Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation :

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/4/1.

Hints

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

Hint 1

Atoms are only rearranged in a reaction. What does that say about total mass?

Hint 2

Start balancing with the group as one unit, then Zn, then H.

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. We balance a chemical equation so that the number of atoms of each element is the same on both sides of the reaction.

    ½ mark

  2. The law is the Law of Conservation of Mass.

    ½ mark

  3. Statement: Mass can neither be created nor destroyed in a chemical reaction. The total mass of the products equals the total mass of the reactants.

    1 mark

  4. Balance the groups and Zn first, then hydrogen:

    Check: Zn 3 = 3, P 2 = 2, O 8 = 8, H 6 = 6.

    1 mark

Answer: To make the atoms of each element equal on both sides; Law of Conservation of Mass; .

Where the marks are

  • Reason: equal number of atoms of each element on both sides (½ mark)
  • Names the law of conservation of mass (½ mark)
  • States the law correctly (1 mark)
  • Correct 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 31/4/1: 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.