Number of moles is the ratio of mass to molar mass.
The molar masses of benzene and toluene are 78 g/mol and 92 g/mol respectively.
Number of moles of benzene =8078=1.026
Number of moles of toluene =10092=1.087
Mole fraction of benzene, XB=1.0261.026+1.087=0.486
Mole fraction of toluene, XT=1−0.486=0.514
PB=PoB×XB=50.71×0.486=24.65 mm Hg
PT=PoTXT=32.06×0.514=16.48 mm of Hg
Total vapour pressure =24.65+16.48=41.13 mm Hg
Mole fraction of benzene in vapour phase is as follows:
YB=24.6541.13=0.60