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

Options

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

Answer

B

Explanation

`(640-600)/(640)=(2.175//M_(2))/(2.175//M_(2)+39//78)`
or `0.0625[(2.175)/(M_(2))+0.5]=(2.175)/M_(2)`
`M_(2)=65.3`