For the dissociation of $Na_2SO_4$,how is the degree of dissociation $\alpha$ used to calculate the van't Hoff factor $(i)$?

$A$ 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 $AB_2 \rightarrow A^{2+} + 2B^{-}$]

Which of the following pairs has the same freezing point?

Which of the following has the minimum freezing point?

The freezing point of an equimolal aqueous solution will be highest for:

$A$ $0.1 \ mol$ of a binary electrolyte undergoes complete dissociation in $250 \ g$ of a protic solvent. If the elevation in boiling point is $1.5 \ K$,the molal elevation constant $(K_b)$ is ............. $K \ kg \ mol^{-1}$.