Why can dew on grass and frost on nearby metal occur on the same night?

Correct answer: Different surfaces can cool to different temperatures

Nearby objects do not always cool at the same rate or reach the same final temperature during one night. Grass, metal, soil, and other materials differ in colour, texture, heat capacity, conductivity, and exposure to the sky and surrounding air. A metal surface may lose heat quickly and fall below freezing, allowing frost to form, while grass in a slightly warmer or more sheltered spot may remain above freezing and collect liquid dew. The two deposits can therefore occur close together under the same general weather conditions.

Option A is correct because different surfaces can cool to different temperatures. Option B is incorrect: water vapour can reach metal through the air. Option C is too absolute, because grass can also receive frost when it becomes sufficiently cold. Option D is wrong because both dew and frost depend strongly on temperature and moisture. The decisive detail is the local temperature of each surface, not simply the air temperature reported for the whole area.