If sodium sulphate is considered to be completely dissociated into cations

If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water $\left(\Delta \mathrm{T}_{\mathrm{f}}\right)$, when $0.01 \mathrm{~mol}$ of sodium sulphate isdissolved in $1 \mathrm{~kg}$ of water, is $\left(\mathrm{K}_{\mathrm{f}}=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$ :-