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With the help of an… (Class 10 Science 2025, Q28a)

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

CBSE Class 10 Science 2025: question 28(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section C, question 28(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28(a) · 3 marks · Short answerMetals and Non-metals

With the help of an activity, explain the conditions under which iron articles get rusted.

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

Design tubes where the nail gets air only, water only, and both.

Hint 2

How can you remove dissolved air from water, and how can you remove moisture from air?

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. Set-up: Take three test tubes labelled A, B and C and place clean iron nails in each. In A, pour some ordinary tap water and cork it, so the nails get both air and water.

    1 mark

  2. In B, pour boiled distilled water, which has no dissolved air, add about 1 mL of oil to stop air dissolving, and cork it. This gives water only. In C, put anhydrous calcium chloride, which absorbs moisture, and cork it. This gives dry air only. (Diagram: three corked tubes. A: nails partly in water with air above. B: nails in boiled water under an oil layer. C: nails above anhydrous in dry air.)

    1 mark

  3. Observation: After a few days, the nails in A rust, but the nails in B and C do not. Conclusion: Iron rusts only when it is exposed to both air (oxygen) and water (moisture) together.

    1 mark

Answer: Iron rusts only when both air (oxygen) and water (moisture) are present (nails rust in tube A only).

Where the marks are

  • Sets up tube A with nails in water and air (1 mark)
  • Sets up tube B (boiled water + oil) and tube C (anhydrous CaCl₂) as controls (1 mark)
  • Observes rust only in A and concludes air and water are both needed (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 paper2025 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.