If two substances A and B have p∘A:p∘B=1:2 and mole fraction in solution = 1 : 2 then mole fraction of A in vapours is

Mole fraction of component A in vapour phase = Partial pressure of A Total vapour pressure =pApA+pBBut pA=pA∘xA and pB=pB∘xB∴Mole fraction of A in vapour phase =pA∘xAp∘xA+pB∘xBGiven, pA∘=1,xA=1,pB∘=2,xB=2On substituting the values, we get Mole fraction of component A in vapour phase=1×11×1+2×2=11+4=15=0.2