The vapour pressure of a pure liquid 'A' is 70 torr at `27^(@)C`. It forms an ideal solution with another liquid B. The mole fraction of B is 0.2 and total pressure of the solution is 84 torr at `27^(@)C`. The vapour pressure of pure liquid B at `27^(@)C` is :

Options

A. 14 torr
B. 56 torr
C. 140 torr
D. 70 torr

Answer

C

Explanation

`p_(A)=(1-0.2)xx70=0.8xx70=56` torr
`p_(B)=84-56=28` torr
`28=0.2xxp_(B)^(0) or p_(B)^(0)=140` torr]