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When an element 'X' reacts… (Class 10 Science 2026, Q23)

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ScienceCBSE Class 10 · Board exam 2026, set 31/1/1 · 1 mark · MCQ

CBSE Class 10 Science 2026: question 23

Set in the CBSE Class 10 board exam of 2026, paper 31/1/1, section B, question 23, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q23 · 1 mark · MCQMetals and Non-metals

When an element 'X' reacts with water, it starts floating. Identify the element 'X':

  1. (A)Potassium
  2. (B)Calcium
  3. (C)Sodium
  4. (D)Iron

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/1/1.

Hints

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

Hint 1

Think about which gas forms and where its bubbles collect.

Hint 2

Look for the metal whose reaction with water is not violent.

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. Calcium reacts less violently with water:

  2. Bubbles of hydrogen gas stick to the surface of the metal, so calcium starts floating. Potassium and sodium react so violently that the hydrogen catches fire, and iron does not react with cold water. Correct option: (B) Calcium.

    1 mark

Answer: Calcium, option (B)

Where the marks are

  • Identifies calcium and the reason (hydrogen bubbles stick to it) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2026 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.