Why does dew form on grass on a cold night?

Correct answer: Water vapour condenses on a cool surface

Direct answer: B, water vapour condenses on a cool surface. During a clear, calm and cold night, grass can lose heat and become cooler than the surrounding air. Air near the grass may then reach its dew point, the temperature at which it cannot retain all its water vapour. Excess vapour changes into tiny liquid droplets on the grass blades; these droplets are called dew. A is wrong because grass does not pull liquid water from the air as the main explanation. B correctly describes the phase change from invisible gas to visible liquid. C is wrong because wind does not create water; strong wind may even interfere with the quiet surface cooling needed for dew. D is wrong because soil is not the direct cause; the essential process is condensation of atmospheric vapour on a cool surface. Memory cue: dew is “air moisture on a cool surface,” not rain and not plant-produced water. Dew should also be distinguished from frost: frost forms as ice when the surface is below freezing, whereas dew is liquid water.