Explanation
- A
The total amount of insolation received at the equator is roughly about 10 times of that received at the poles.
Equator gets ~10× polar insolation. Polar night/day and geometry do not make a clean tenfold total.
- B
Infrared rays constitute roughly two- thirds of insolation.
Infrared is two-thirds of insolation. Solar energy peaks in visible; IR is a large but not this stock fraction as keyed.
- C
Infrared waves are largely absorbed by water vapour that is concentrated in the lower atmosphere.
Water vapour in the lower air absorbs much of the outgoing / long-wave infrared.
- D
Infrared waves are a part of visible spectrum of electromagnetic waves of solar radiation.
Infrared is part of the visible spectrum. IR is adjacent to visible, not inside it.
Summary. Official key is (c). Water vapour, concentrated in the lower troposphere, is a strong absorber of infrared. Insolation is not ‘ten times’ at the equator versus poles as a total; IR is not two-thirds of insolation in the sense of (b); infrared is not visible light.
Same topic · past papers
UPSC has asked this before
These previous-year questions sit on the same topic. Open one to practise the earlier ask.
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