1.

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

Answer» Correct Answer - D
`(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].


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