$11\mathrm{.}4$ An inverted U$-$tube of cross$-$sectional area $100m{m}^2$ has $100mg$

of sodium chloride at the bottom of one arm and $5{10}^{-6}{m}^3$ of water

in the other, the remaining space being filled with water vapour. It is

kept at a constant temperature of $20C$ and the water vapour condenses

on the salt side to form a salt solution. What is the difference in the

levels of the liquids in the arms when the system reaches equilibrium?

$[$Relative molecular mass of sodium chloride $=58\mathrm{.}4.$ Vapour pressure

of water at $20C=17\mathrm{.}5mmHg.]$