The vapour pressure of a solvent decreases by 10 mm of Hg when a non-volatile solute is added to it. The mole fraction of the solute in solution is equal to 0.2. What should be the mole fraction of solvent if the decrease in vapour pressure is to be 20 mm Hg?

Explanation

`X_(solute)=0.2` when `P_A^0-P_A=10 mm hg`
`X_(solute)=0.2=4` when `P_A^0-P_A=20 mm hg`
`X_(solvent)=1-X_(solute)=1-0.4=0.6`