Clouds form when water vapor in the atmosphere cools to
a) its dew point
b) its relative humidity
c) its convection point
d) its precipitation

The answer to the question: Clouds form when water vapor in the atmosphere cools to:, would be, A: Its dew point.

Explanation:

Clouds are simply the visible condensation of the warm air that rises into the cooler atmosphere. Once this happens, with the moisture carried in the warm air, the cooler atmosphere will bring down the temperature of the air, and the water inside it in form of vapor, till it reaches dew point. Once there, the air condenses into either water dropplets, or crystals, making clouds look like formed pieces of cotton. If condensation is light, the clouds will appear white, and clear, as condensation gets higher, and temperatures change, the cloud will get darker, as it gets heavier with water. At its breaking point, water will come down now condensed either as rain, or ice, depending on temperatures.