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. 150
C. 1500
D. 1.5

Answer

B

Explanation

`(P^(0)-P)/(P^(0)) = ( W_(B)M_(A))/(M_(B)W_(A))`
`M_(B) = ( 2 xx78 xx 750 )/( 10 xx78) = 150 `