In water saturated air, the mole fraction of water vapour is 0.02. If the total pressure of the saturated air is 1.2 atm, the partial pressure of dry air is

Mole fraction of water vapour = 0.02
Mole fraction of dry air = 1 – 0.02 = 0.98
Total pressure of saturated air = 1.2 atm
Using Dalton’s law of partial pressure,

${\mathrm{P}}_{\text{Dry air }}={\mathrm{P}}_{\text{Total }}{\mathrm{x}}_{\text{Dry air }}=1.2\times 0.98$

= 1.176 atm