What primary process leads to the formation of clouds?

The formation of clouds primarily occurs due to the condensation of water vapor. When warm air rises, it cools, and as it does, the capacity of the air to hold water vapor decreases. This cooling causes water vapor to condense into tiny water droplets or ice crystals, depending on the temperature. These droplets or crystals cluster together to form clouds.

While evaporation is an essential process that provides the water vapor necessary for cloud formation, it is the subsequent condensation that directly leads to the creation of clouds. Precipitation refers to the process by which water falls from clouds as rain, snow, or other forms, and transpiration is the release of water vapor from plants, both of which occur after clouds have formed. Therefore, the correct answer focuses on the key phase that converts vapor back into liquid or solid form to create cloud structures in the atmosphere.