Question

which atmospheric gas plays the biggest role in weather and forms clouds? water vapor carbon dioxide methane oxygen

Explanation:

Water vapor is crucial in weather processes. It undergoes phase changes (evaporation, condensation) which are fundamental to cloud formation. Clouds are formed when water vapor condenses around tiny particles. Carbon dioxide, methane, and oxygen do not play as direct and significant a role in cloud - formation and weather dynamics as water vapor.

Answer:

water vapor