The vapour pressure of pure benzene at a certain temperature is `640 mm Hg`. A non-volatile solid weighing `2.175g` is added to `39.0g` of benzene. The vapour pressure of the solution is `600mm Hg`. What is the molar mass of the solid substance?

Options

A. `6.96`
B. `65.3`
C. `63.8`
D. None of these

Answer

B

Explanation

`(640-600)/(640)=(2.715//m_(1))/((2.175)/(m_(1))+(39)/(78))`
`rArr 0.0625xx((2.175)/(m_(1))+0.5)=(2.175)/(m_(1))`
`rArr 0.9375xx(2.175)/(m_(1))=0.6225xx0.5`
`:.m_(1)=65.3`
Hence, (B) is the correct answer.