Which of the following is the main cause of rainfall?

Question

Accepted Answer

The correct option is 4: Both evaporation & condensation.

Rainfall is a result of the entire water cycle, which depends fundamentally on the two physical processes of evaporation and condensation working in sequence. Evaporation, the process where water converts from a liquid state into water vapor (gas) due to heat energy, is necessary to lift the moisture from the Earth's surface (oceans, lakes, and soil) into the atmosphere. This gaseous moisture then rises, cools, and undergoes condensation, which is the process where water vapor turns back into liquid water droplets or ice crystals, forming clouds. When these cloud droplets coalesce and become too heavy for the air currents to hold, they fall back to the Earth as precipitation (rainfall). Therefore, neither evaporation nor condensation alone causes rainfall; it is their combined, cyclic operation that drives the precipitation process.

The incorrect option is 1: Filteration.
Filtration is a purification process used to separate solid particles from a liquid or gas by passing the mixture through a porous material. This process is used in water treatment and cleaning, but it has no role in the atmospheric mechanisms that cause rain to fall.

The incorrect option is 2: Evaporation.
While evaporation is the critical first step in the water cycle, supplying the necessary moisture to the atmosphere, it only changes liquid water to water vapor. Evaporation itself does not cause rainfall; it actually takes water away from the surface.

The incorrect option is 3: Condensation.
Condensation is the process that forms clouds by turning water vapor into liquid droplets. However, condensation cannot occur without the preceding step of evaporation, which provides the water vapor in the first place. Therefore, while condensation is the immediate process that forms the rain-bearing clouds, the entire "cause" of rainfall requires both steps.