Why does dew formation decrease when clouds cover the sky at night?

Correct answer: Clouds reduce cooling by trapping terrestrial longwave radiation

The correct answer is A. On a clear night, the ground loses energy by emitting terrestrial longwave radiation and can cool substantially. If the surface cools to its dew point, water vapour may condense as dew. Clouds absorb and re-emit longwave radiation and therefore reduce the net loss of heat from the ground. The surface usually does not cool as efficiently, so it is less likely to reach the dew point and dew formation decreases. B is wrong because clouds do not remove all moisture from the air. C is wrong because cloud cover does not necessarily make the ground freeze; it often reduces radiative cooling. D is wrong because clouds do not destroy condensation nuclei. Memory cue: “clear nights cool strongly; cloudy nights act like a thermal blanket.”