The vapour presure of benzene at `80^(@)C` C is lowered by 10 mm by dissolving 2g of a non -volatile substance in 78 g of benzene. The vapour pressure of pure benzene at `80^(@)C` is 750 mm. The molecular masss of the substance will be:

Options

A. 15
B. 150
C. 1500
D. 148

Answer

D

Explanation

`(P^(@)-P_(s))/(P^(@))=X_("Benzene")`
`implies(750-740)/750=(2//M)/(2/M+78/78)`
On solving `M=148`