Skip to content

State giving reason for the… (Class 10 Science 2024, Q28b)

questionbuddy.in/q/cbse-10-science-2024-31-3-1-q28b-giving-change-appearance-observed-metal

ScienceCBSE Class 10 · Board exam 2024, set 31/3/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 28(b)

Set in the CBSE Class 10 board exam of 2024, paper 31/3/1, section C, question 28(b), for 3 marks. Try it first; the hints and our step-by-step solution are below.

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

State giving reason for the change in appearance observed when each of the following metal is exposed to atmospheric air for some time :
(i) Silver,
(ii) Copper and
(iii) Iron

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/3/1.

Hints

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

Hint 1

This is corrosion: think of old silver jewellery, copper vessels and iron gates.

Hint 2

Which gas or vapour in air reacts with each metal: H₂S, moist CO₂, or O₂ with water?

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. (i) Silver: Shiny white silver turns black (tarnishes).

    ½ mark

  2. Reason: It reacts with hydrogen sulphide in air to form a coating of silver sulphide, .

    ½ mark

  3. (ii) Copper: Reddish-brown copper gains a green coating.

    ½ mark

  4. Reason: It reacts with moist carbon dioxide in air to form basic copper carbonate, .

    ½ mark

  5. (iii) Iron: Grey iron becomes covered with a reddish-brown flaky layer.

    ½ mark

  6. Reason: In the presence of moist air (oxygen and water), iron rusts, forming hydrated iron(III) oxide, .

    ½ mark

Answer: (i) Silver turns black (Ag₂S formed). (ii) Copper turns green (basic copper carbonate formed). (iii) Iron gets a reddish-brown coating (rust, hydrated iron oxide).

Where the marks are

  • Silver: white to black (½ mark); silver sulphide formed (½ mark)
  • Copper: reddish-brown to green (½ mark); basic copper carbonate formed (½ mark)
  • Iron: grey to reddish-brown (½ mark); rust/iron oxide formed (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 paper2024 board paper, set 31/3/1: 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.