Less dew is formed on cloudy nights because

Answer: (c) In cloudy nights the radiation takes place very slowly

Clouds slow the loss of heat, so the ground doesn’t cool enough to form much dew.

The idea

Dew needs a surface cool enough for nearby water vapour to condense. On a clear night, the surface can lose heat rapidly by infrared radiation. Clouds add downward infrared energy and reduce that net loss. The surface may then fail to reach dew point even though the air contains moisture.

Surface emits infrared after sunset → Clouds absorb some outgoing energy → They emit part of that energy downward → Net surface cooling slows → Surface remains farther from dew point → Less dew tends to form

Why the others are wrong

(d) Reversed.

Elimination technique

Dew forms on a surface, so clouds cannot explain less dew by absorbing “falling dew”. The option saying faster radiation would favour stronger cooling and more dew; the reduced-cooling explanation in (c) fits.

Also know

Dew is not rain that falls from clouds: it condenses directly on objects. Fog consists of suspended droplets, and frost is an ice deposit or frozen condensation. Light winds can replenish vapour without disrupting cooling, but strong mixing often limits dew. Clouds reduce the likelihood of strong cooling; they do not rule out dew in every weather situation.