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

Options

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

Answer

D

Explanation

`(P_(0)-P_(s))/(P_(s))=(wxxM)/(mxxW)`
`(10)/((750-10))=(2xx78)/(mxx78)`
`:. m= 148`,
Note : [`m` comes `150` if formula `(P_(0)_p_(s))/(P_(o))=(wxxM)/(mxxW)` is used. But this is only for dilute solutions].