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

Options

A. 15
B. 14.8
C. 1500
D. 148

Answer

D

Explanation

`(P_(1)^(@)-P)/P_(1)^(@)=(W_(2) xx M_(1))/(M_(2) xx W_(1))`
`10/((750-10))=(2 xx 78)/(M_(2) xx 78) :. M_(2) = 148`