(i) We can determine whether air is saturated with vapour or not on the basis of relative humidity.
(ii) Relative humidity is the ratio of actual mass of vapour content in air for given volume and temperature to that required to make air saturated with vapour at that temperature.
(iii) If relative humidity is 100%, the air is saturated with vapour. This is called dew point.
(iv) If its value is less than 100%, then air is unsaturated.
