Normally, the temperature decreases with the increase in height from the Earth's surface, because 1) the atmosphere can be heated upwards only from the Earth's surface 2) there is more moisture in the upper atmosphere 3) the air is less dense in the upper atmosphere Select the correct answer using the codes given below:

The correct answer is C, that is, statements 1 and 3 only. The core concept is the tropospheric lapse rate. The atmosphere is mainly heated from below. Sunlight passes through the air largely unabsorbed and warms the ground, and the ground then re-radiates heat as longwave radiation, which warms the air in contact with it. So the lowest layers are warmest and temperature falls with height, at roughly 6.5 degrees Celsius per km in the standard atmosphere. This is statement 1, and it is correct.

Statement 3 is also correct. Upper air is thinner, so it holds less heat per unit volume and absorbs less terrestrial radiation. Less dense air also means less heat is retained, so temperature drops.

Statement 2 is wrong. Water vapour is concentrated near the surface and falls off steeply with height, so the upper atmosphere is drier, not moister. Moisture is not the reason for the lapse rate.

For Mains, this lapse rate explains convection, cloud formation and the stability of the lower atmosphere. You will also meet it when you discuss temperature inversions and air pollution dispersal.

Trap: aspirants often pick option D because "thin air" and "moisture" sound like plausible causes. Check each statement against the physics of heating: the heat source is the ground, not the air itself.