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Observe the following… (Class 10 Science 2025, Q28A)

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ScienceCBSE Class 10 · Board exam 2025, set 31/5/1 · 3 marks · Short answer

CBSE Class 10 Science 2025: question 28(A)

Set in the CBSE Class 10 board exam of 2025, paper 31/5/1, 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

Observe the following diagram showing an experiment to determine the conditions under which a metal 'M' corrodes. List your observations in each of the three cases A, B and C with reason, if the metal 'M' is generally protected against corrosion by the method of galvanisation.

Figure in the paper: Three test tubes labelled A, B and C. A and B contain moist air above a metal 'M' sample partly immersed in oil at the bottom; in B the moisture level is higher. C contains dry air above metal 'M' with anhydrous calcium chloride (granules) at the bottom instead of oil. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/5/1.

Hints

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

Hint 1

Galvanisation protects iron, so M is iron; rusting needs both air and moisture.

Hint 2

In each tube, check which part of the metal touches moist air and which part is shielded by oil or dry 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. Test tube A: Metal M (iron, the metal usually protected by galvanisation) corrodes partly. The part above the oil is exposed to moist air and rusts. The part dipped in oil is cut off from air and moisture, so it does not rust.

    1 mark

  2. Test tube B: Metal M does not corrode, because it is fully inside the oil and not exposed to moist air.

    1 mark

  3. Test tube C: Metal M does not corrode, because anhydrous calcium chloride absorbs moisture and the air is dry. Rusting needs both air and water.

    1 mark

Answer: A: partly corroded (only the part outside the oil); B: no corrosion (covered by oil); C: no corrosion (dry air due to anhydrous CaCl₂).

Where the marks are

  • A: partial corrosion with reason (½ + ½ mark)
  • B: no corrosion, metal shielded by oil from moist air (½ + ½ mark)
  • C: no corrosion, moisture absent (½ + ½ 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 31/5/1: 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.