Question

what is relative humidity? when is the air said to be saturated? what happens when the temperature of saturated air drops suddenly?

Answer 1

relative humidity; the amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature.  

Air is said to be saturated when the amount of water vapor in the air is the maximum possible at an existing temperature and pressure.   
 
 A drop in air pressure and temperature is a tell-tale sign of an approaching cold front. ... Ahead of a cold front lies an area of warm, moist air. ... The passing of the front will be signaled by asudden, steep drop in temperatures.

Answer 2

Answer:

When the air contains as much water vapour as it can hold only at given temperature it is said to be saturated.