AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Correct Option: C — Scattering of sunlight by air particles is not prominent at such heights.
At very high altitudes, the atmosphere is very thin, so scattering of sunlight by air particles is negligible, making the sky appear dark.
The textbook (Section 10.6.2) explicitly states: "The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights." The blue colour of the sky is caused by scattering of sunlight by fine atmospheric particles. At very high altitudes, the atmosphere is too thin for significant scattering to occur, so no scattered blue light reaches the eye — the sky looks dark. Options A, B, and D are incorrect explanations not supported by the textbook.