Why are dewdrops not formed on a cloudy night?

Option (B) is correct because clouds act as a thermal blanket, reflecting outgoing long-wave terrestrial radiation back toward the Earth's surface, which prevents the ground from cooling down to the dew point. While option (A) is tempting as clouds do absorb some radiation, the primary reason the surface stays warm is the re-radiation and reflection of heat back downwards. The core concept tested is the Earth's heat budget and the specific atmospheric conditions—namely clear skies and calm air—required for nocturnal cooling and condensation.