Why are dew droplets often first visible on grass, leaves, and metal?

Correct answer: Because these surfaces cool quickly and provide condensation sites

The correct answer is D. At night, grass, leaves, and exposed metal can lose heat by terrestrial radiation and cool rapidly. If their surface temperature falls to or below the dew point while remaining above freezing, nearby water vapour condenses into liquid droplets on them. Their surfaces therefore act as places where condensation becomes visible. A is wrong because grass, leaves, and metal do not create the atmospheric water vapour responsible for dew; the vapour is already present in the air. B is wrong because these objects do not always attract clouds. C is wrong because dew formation has no role in stopping rainfall. D is the best answer because it identifies both the rapid cooling of exposed surfaces and the visible site of condensation. Memory cue: “cold exposed surface plus moist air makes dew.”