The vapour pressure of a pure liquid A is 70 torr at 300K. It forms an ideal solution with another liquid B. The mole fration of B in the solution is 0.2 and total pressure of solution is 84 torr at 300K. The vapour pressure of pure liquid B at `26^(@)C` is

Options

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

Answer

C

Explanation

`P_(A) = X_(A) xx P_(A)^(@)=(1-0.2) xx70=56 ` torr,
`P_(B)=P_("total")-P_(B)=84-56=28` torr
`P_(B)=X_(A) xx P_(B)^(@)` or
`p_(B)^(@)= P_(B)//X_(B)=28//0.2=140` torr