The mole fraction of toluene in the vapour phase which is in equilibrium with a solution of benzene `(P_(B)^(@)=120 "torr")` and toluene `(P_(T)^(@)=80 "torr")` having `2.0 mol` of each, is

Options

A. `0.50`
B. `0.25`
C. `0.60`
D. `0.40`

Answer

D

Explanation

`P_(T)=X_(A)P_(A)^(@)+X_(B)P_(B)^(@)`
`=((2)/(4))xx80+((2)/(4))xx120=100` Torr
Now mole fraction in vapour phase `=(X_(A)P_(A)^(0))/(P_(T))=(40)/(100)=0.4`.