On which surface can frost be more clearly visible?

Correct answer: Cold grass and leaves

Answer: A, cold grass and leaves. Frost is a deposit of ice formed when an exposed surface becomes sufficiently cold, usually at or below the freezing point. Water vapour may deposit directly as ice crystals, or a thin layer of dew may freeze. Grass and leaves lose heat efficiently during a clear night because they are exposed to the open sky, so they can cool more than nearby air or sheltered objects. Their fine surfaces make the white crystals easy to notice. Option B is wrong because hot sand is not cold enough for frost at that time. Option C is wrong because a wall warmed by midday sunlight is also too warm; frost is associated mainly with night-time cooling. Option D is wrong because warm seawater does not normally provide a freezing surface. Remember that frost is not simply any moisture; it is moisture associated with freezing conditions. Memory cue: exposed, cold vegetation is a classic place to look for frost.