Which surface can be more helpful for dew formation?

Correct answer: Cold grass surface

Direct answer: C, a cold grass surface. Dew forms when moist air touches a surface that has cooled to the dew point, so water vapour changes into tiny liquid droplets. At night, grass often loses heat and becomes cool, allowing these droplets to collect on its blades. A is wrong because hot iron does not normally cool moist air to the dew point. B is wrong because very hot sand encourages evaporation rather than condensation. D is wrong because a burning rock is extremely hot and cannot normally collect dew. Remember: dew is liquid water on a cool surface; frost is the icy form on a freezing surface. Thus cold grass is the most suitable choice.