Two liquids X and Y form an ideal solution. The mixture has a vapour pressure of 400 mm at 300 K when mixed in the molar ratio of 1 : 1 and a vapour pressure of 350 mm when mixed in the molar ratio of 1 : 2 at the same temperature. The vapour pressures of the two pure liquids X and Y respectively are

Ideal sol. (1)                                                        Ideal sol. (2)   Ptot=400mm                                                          Ptot=350nA:nB =1:1                                                             nA:nB =1:2XA=1/2 , XB=1/2                                                       XA=1/3 , XB=2/3                                                                                                             By solving (1) & (2)  ;    we get