A solution of two substances A and B was formed (mole fractions are xA & xB). It was found that the mole fraction of A in vapour phase (yA) was twice of xA. This is only possible if
PoA>PoB
xA=PoA−2PoB2(PoA−PoB)
PtyA=PA⇒yA=PAPt=PoAxAPoAxA+PoB(1−xA)⇒2xA=PoAxA(PoA−PoB)xA+PoB(yA=2xA)⇒2(PoA−PoB)xA+2PoB=PoA⇒xA=PoA−2PoB2(PoA−PoB)
Also, more mole fraction in vapour phase clearly means PoA>PoB