The molar volume of liquid benzene (density = 0.877 g mL−1 ) increases by a factor of 2750 as it vaporises at 20∘C and that of liquid toluene (density 0.867 g mL−1 ) increases by a factor of 7720 at 20∘C . A solution of benzene and toluene at 20∘C has a vapour pressure of 46.0 torr. Find the mole fraction of benzene in the vapour above the solution.