Explanation

Option B is correct: Dew formation requires the terrestrial ground surface and nearby air to cool down below the dew point temperature via unobstructed nocturnal radiational cooling:

– On clear, cloudless nights, longwave terrestrial infrared radiation emitted by the Earth escapes directly into space, chilling the surface.
– On a cloudy night, dense cloud cover acts like a blanket that absorbs and reflects back the Earth’s outgoing longwave radiation towards the surface.
– Consequently, the ground remains warm and cannot cool sufficiently to reach the saturation dew point needed for water vapor to condense into droplets.

Therefore, dewdrops do not form because Clouds reflect back the Earth’s radiation — Option B.