The correct option is 1 and 3 only.
Explanation
Dew is a form of condensation where moisture deposits in the form of water droplets on cooler surfaces of solid objects rather than on nuclei in the air. It occurs when the temperature of the air touching the surface falls below the dew point.
Statement-wise Analysis:
- Statement 1 is Correct: Dew forms when moisture is deposited on cold surfaces such as stones, grass blades, and plant leaves. This happens because these surfaces lose heat through radiation more rapidly than the surrounding air, causing the air in contact with them to cool and condense its moisture.
- Statement 2 is Incorrect: The ideal conditions for the formation of dew are a clear sky, calm air, high relative humidity, and cold, long nights. A cloudy sky prevents the ground from cooling effectively due to the greenhouse effect (clouds trap terrestrial radiation). Strong winds mix the air, preventing the layer immediately in contact with the ground from cooling sufficiently to reach the dew point.
- Statement 3 is Correct: For dew to form, the dew point must be above the freezing point. If the dew point is at or below the freezing point, the excess moisture deposits in the form of minute ice crystals, which is known as frost, not dew.
Key Takeaway:
Dew formation requires clear skies, calm air, and a dew point above freezing (0°C). If the dew point is below freezing, the condensation results in frost.