With reference to the Earth's atmosphere, which one of the following statements is correct?

Answer: (c) Infrared waves are largely absorbed by water vapour that is concentrated in the lower atmosphere.

Water vapour in the lower atmosphere absorbs much of the infrared.

The idea

Insolation means incoming solar radiation, which includes ultraviolet, visible and infrared wavelengths. A gas need not absorb all wavelengths equally. Water vapour absorbs strongly in several infrared bands and is concentrated mainly in the lower atmosphere. Visible light is only one part of the solar spectrum.

Why the others are wrong

(a) The equator gets only about 2–3 times the polar insolation in a year, not 10.

(b) Infrared is about half of insolation, not two-thirds.

(d) Infrared is not part of the visible spectrum.

Elimination technique

Infrared lies beyond the red end of visible light, so (d) fails by definition. The claim of a tenfold equator-to-pole difference is too large for the broad annual comparison, and two-thirds is not the usual infrared share of solar energy.

Also know

The Sun emits mainly short-wave energy, while the cooler Earth emits mainly long-wave infrared. Ozone is important for ultraviolet absorption; carbon dioxide and water vapour absorb infrared. Insolation per unit area also depends on Sun angle, day length and cloud cover. Scattering redirects radiation, whereas absorption transfers its energy to matter.