ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 1 mark · MCQ

CBSE Class 10 Science 2025: question 1

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

Q1 · 1 mark · MCQChemical Reactions and Equations

Electrolysis of water is a decomposition reaction. The mass ratio $(M_{H} : M_{O})$ of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :

(A) $8 : 1$
(B) $2 : 1$
(C) $1 : 2$
(D) $1 : 8$

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

Write the balanced equation for the decomposition of water.

Hint 2

Multiply the number of moles of each gas by its molar mass (H₂ = 2 g, O₂ = 32 g).

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.

Balanced equation for electrolysis: $2 H_{2} O \to 2 H_{2} + O_{2}$
Mass of hydrogen $= 2 \times 2 = 4$ g. Mass of oxygen $= 1 \times 32 = 32$ g.
$M_{H} : M_{O} = 4 : 32 = 1 : 8$ , so the answer is option (D).
1 mark

Answer: 1 : 8, option (D)

Where the marks are

Chooses option (D) 1 : 8 (1 mark)

Revise the chapter

Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)

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.

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CBSE Class 10 Science 2025: question 1

Hints

Step-by-step solution

Revise the chapter

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