$2\text{ g}$ of $\text{Na}_2\text{SO}_4$ is dissolved in $50\text{ g}$ of water to form a solution. Calculate the freezing point of this solution, assuming $\text{Na}_2\text{SO}_4$ undergoes complete dissociation. [Given : Molar mass of $\text{Na}_2\text{SO}_4 = 142\text{ g mol}^{-1}$, $\text{K}_\text{f}$ for water $= 1\cdot86\text{ K kg mol}^{-1}$]