how rain occurs?

Answer 1

If the air temperature inside a cloud is above freezing point,water droplets merge and grow until they are heavy enough to fall, reaching the ground as rain.
If ice crystals are present in a cloud,they bond together until large enough to fall.While falling they either remain frozen,reaching the ground as snow,or they melt ,reaching the ground as rain.

Answer 2

Precipitation.

In meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface.