If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, what is the change in freezing point of water$(\Delta T_f)$,when 0.02mol of sodium sulphate is dissolved in 1kg of water,is $(K_f=1.86Kkgmol^{-1})$?

Question

$\begin{array}{1 1}(a)\;0.0372K\\(b)\;0.112K\\(c)\;0.0744K\\(d)\;0.0186K\end{array}$