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Give reasons : (Class 10 Science 2025, Q25a)

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ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 25(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, section B, question 25(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q25(a) · 2 marks · Very short answerCompetency-basedThe Human Eye and the Colourful World

Give reasons :

  1. (i)

    The sky appears dark to passengers flying at very high altitude.

    1 mark
  2. (ii)

    'Danger' signal lights are red in colour.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

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

Hint 1

The blue colour of the sky comes from scattering by particles of air. What happens when there is almost no air?

Hint 2

How does scattering depend on wavelength, and which colour has the longest wavelength?

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) At very high altitudes there is almost no atmosphere, so there are hardly any particles to scatter sunlight. Since scattering is not prominent, no scattered light reaches the eye and the sky looks dark.

    1 mark

  2. (ii) Red light has the longest wavelength in the visible spectrum, so it is scattered least by fog, smoke and dust. It therefore travels farthest and can be seen from a long distance.

    1 mark

Answer: (i) Negligible scattering at high altitude due to very few particles; (ii) red light is scattered least because of its longest wavelength.

Where the marks are

  • Scattering of light is negligible at such heights (1 mark)
  • Red light is scattered least by fog/smoke because it has the longest wavelength (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from The Human Eye and the Colourful World, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/6/1: 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.