Given, pA∘‌=200‌mm‌Hg pB∘‌=400‌mm‌Hg Mole fraction of A in solution =χA=0.7 Mole fraction of B in solution =χB=0.3 p‌Total ‌‌=χApA∘+χBpB∘ ‌=(0.7×200)+(0.3×400)=140+120 ‌=260‌mm‌Hg Mole fraction of B in vapour phase =‌