3g of urea is dissolved in 45g of `H_(2)O`. The relative lowering in vapour pressure is

Options

A. 0.05
B. 0.04
C. 0.02
D. 0.01

Answer

C

Explanation

The relative logwering of vapour pressure is given by
`(P^(o) - P_(S))/(P^(o)) = (n_(2))/(n_(1) + n_(2))`
For a dilute solution, `n_(2)` can be neglected, then
`(P^(o) - P_(S))/(P^(o)) = (n_(2))/(n_(1)) = (3//60)/(45//18)` = 0.02 mm
(Where, `n_(2)` for urea and `n_(1)` for water)