What factor is essential for the formation of clouds?

The formation of clouds is fundamentally linked to the presence of moisture in the air. For clouds to develop, water vapor must be present in sufficient quantities. When air containing moisture rises, it cools due to lower temperatures at higher altitudes. As the air cools, the capacity to hold water vapor decreases, leading to condensation of the water vapor into tiny water droplets or ice crystals, depending on the temperature. These droplets or crystals cluster together, forming clouds.

The other factors mentioned do not play a direct role in cloud formation. Cool temperatures alone are insufficient without moisture; they serve as a catalyst for condensation but cannot create clouds without the presence of water vapor. Strong solar radiation can affect temperature and evaporation rates but does not directly lead to cloud formation. Sustained wind gusts may aid in the movement of air masses but are not essential for the actual process of cloud formation. Without moisture, clouds cannot form, making the presence of moisture in the air the key factor.