Which process is primarily responsible for the formation of clouds?

The primary process responsible for the formation of clouds is the condensation of water vapor in the atmosphere. Clouds form when water vapor rises, cools, and changes back into liquid water droplets or ice crystals. As warm air rises, it expands and cools; when it cools to its dew point, the water vapor present in the air condenses upon tiny particles, such as dust or pollen, which act as nuclei. This accumulation of water droplets or ice crystals then forms visible clouds.

The other processes listed, while they play roles in the overall water cycle, do not directly lead to cloud formation. Sedimentation of dust particles involves the settling of solid particles and does not contribute to cloud creation. The evaporation of ocean water is a vital component of the water cycle, but evaporation alone does not create clouds; it is the subsequent condensation of that vapor that leads to cloud formation. Melting of ice in the atmosphere refers to a phase change that might contribute to humidity but does not actively participate in cloud formation in the same way that condensation does. Thus, condensation is the key process that leads to the visible manifestation of clouds in the sky.