$MX_{2}$ dissociates into $M^{2+}$ and $X^{-}$ ions in an aqueous solution,with a degree of dissociation $(\alpha)$ of $0.5$. The ratio of the observed depression of freezing point of the aqueous solution to the value of the depression of freezing point in the absence of ionic dissociation is

$A$ compound contains $1.08 \ mol$ of $Na, 0.539 \ mol$ of $Cu$ and $2.16 \ mol$ of $F$. Its aqueous solution shows osmotic pressure which is three times that of urea having the same molar concentration. The formula of the compound is:

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

$17.4\% \text{ (mass/volume) } K_2SO_4$ solution at $27^\circ C$ is isotonic to $5.85\% \text{ (mass/volume) } NaCl$ solution at $27^\circ C$. If $NaCl$ is $100\%$ ionized,what is the $\%$ ionization of $K_2SO_4$ in aqueous solution? [Atomic weights: $K = 39, Na = 23, S = 32, O = 16, Cl = 35.5$]

$A$ $0.2 \, m$ aqueous solution of a weak acid $(HX)$ is $20 \% $ ionised. The freezing point of this solution is .............. $^o C$ (Given ${K_f} = 1.86 \, ^o C/m$ for water)

Which of the following will have the lowest vapor pressure?