Which of the following solutions will show the maximum depression in freezing point when the concentration is $0.1 \, M$?

$0.004 \ M$ $Na_2SO_4$ solution is isotonic with $0.01 \ M$ glucose solution,then the degree of dissociation of $Na_2SO_4$ is ........... $\%$.

$A$ $0.2 \, m$ aqueous solution of a weak acid $(HX)$ is $20 \%$ ionised. The freezing point of this solution is .......... $^oC$. ($K_f = 1.86 \, K \cdot kg \cdot mol^{-1}$ for water) :-

$A$ solution containing $10 \ g$ of an electrolyte $AB_2$ in $100 \ g$ of water boils at $100.52^{\circ} C$. The degree of ionization of the electrolyte $(\alpha)$ is............ $\times 10^{-1}$.
(nearest integer)
[Given : Molar mass of $AB_2 = 200 \ g \ mol^{-1}$,$K_{b}$ (molal boiling point elevation constant of water) $= 0.52 \ K \ kg \ mol^{-1}$,boiling point of water $= 100^{\circ} C$;
$AB_2$ ionises as $AB_2 \rightarrow A^{2+} + 2B^{-}$]

The freezing point of equimolal aqueous solution will be highest for

Which of the following has the lowest freezing point?