Which of the following $0.1 \ M$ solutions will exhibit the minimum freezing point?

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

When $HgI_2$ is added to an aqueous solution of $KI$,then the:

The experimental molecular weight of an electrolyte will always be less than its calculated value because the value of Van't Hoff factor $i$ is

$A$ sample of water is found to contain $5.85 \% \left(\frac{w}{w}\right)$ of $AB$ (molecular mass $58.5$) and $9.50 \% \left(\frac{w}{w}\right)$ $XY_2$ (molecular mass $95$). Assuming $80 \%$ ionisation of $AB$ and $60 \%$ ionisation of $XY_2$, the freezing point of the water sample is: [Given, $K_f$ for water $= 1.86 \ K \ kg \ mol^{-1}$, freezing point of pure water $= 273 \ K$ and $A, B, X, Y$ are monovalent ions.] (in $K$)

For $0.01 \ M$ solutions of urea,$NaCl$,and $Na_2SO_4$,the ratio of their depression in freezing point is .......