If the total vapour pressure of the liquid mixture A and B is given by the equation : P=180 XA+90 then the ratio of the vapour pressure of the pure liquids A and B is given by:

As we know PT=PAoXA+PBoXB=PAoXA+PBo(1−XA)=(PAo−PBo)XA+PBo    .....(1)But from question, PT=180 XA+90       .....(2)Equating equation (1) and (2) ∴ PAo−PBo=180PBo=90; PAo=180+90=270PAoPBo=27090=3:1