At 80∘C the vapour pressure of pure liquid 'A' is 520 mm Hg and that of pure liq 'B' is 1000 mm Hg. If mixture of both liquids from ideal solution and boils at 80∘C and 1 atm pressure, the mole fraction of 'A' in the liquid mixture is:
0.5
P∘AXA+P∘BXB=Pmis
(520)XA+(1000)(1−XA)=760
520XA−1000XA=760−1000
−480XA=−240
∴XA=12=0.5