Predict the mole fraction of b in the vapor produced when a mixture of 0.70 mole fraction of a and 0.30 mole fraction of b boils.

Mole fraction of a component in a solution is the ratio of the number of moles of that component to the total number of moles of all component in a solution.

total moles = 0.30 + 0.70=1.00

mole fraction of b={ (0.30 x100) / (1 x100) }=3/10