20 % of acetic acid is dissociated when its 5 g is added to 500 mL of water. The depression in freezing point of such water is ____ × 10^-3^° C.…

$\displaystyle 20 \%$ of acetic acid is dissociated when its $\displaystyle 5$ g is added to $\displaystyle 500$ mL of water. The depression in freezing point of such water is $\displaystyle \_\_\_\_$ $\displaystyle \times 10^{-3}{ }^{\circ} \mathrm{C}$. Atomic mass of C, H and O are $\displaystyle 12$, $\displaystyle 1$ and $\displaystyle 16$ a.m.u. respectively. [Given : Molal depression constant and density of water are $\displaystyle 1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ and $\displaystyle 1 \mathrm{~g} \mathrm{~cm}^{-3}$ respectively.