What atmospheric conditions are required for rain to occur?

Rain formation is fundamentally dependent on a combination of sufficient moisture in the atmosphere, a cooling process that allows the air to become saturated, and the presence of condensation nuclei, which are tiny particles that facilitate the coalescence of water vapor into droplets.

When warm air containing moisture rises, it expands and cools. As the air cools, it can no longer hold as much moisture, leading to a point of saturation. This saturation encourages the water vapor to condense around the condensation nuclei, resulting in the formation of cloud droplets. When these droplets combine and grow large enough, they overcome air resistance and fall as precipitation — which we recognize as rain.

This process highlights the importance of those three specific conditions: adequate moisture ensures there is enough water vapor available, cooling air is critical for reaching the saturation point, and condensation nuclei enable the transition of vapor to liquid droplets. Other options do not correctly represent the necessary atmospheric conditions for rain, as they either focus on elements that do not directly contribute to precipitation or present scenarios that are not conducive to rain formation.