Which of the following equimolar aqueous solutions has the highest freezing point?

The van't Hoff factor for $Ca(NO_3)_2$ is ...... .

At $25 \ ^oC$,the highest osmotic pressure is exhibited by $0.1 \ M$ solution of

What is the freezing point (in $^\circ C$) of a solution containing $0.1 \ g$ of $K_3[Fe(CN)_6]$ (molar mass = $329 \ g \ mol^{-1}$) in $100 \ g$ of water? (Given $K_f = 1.86 \ K \ kg \ mol^{-1}$)

$5 \ g$ of $Na_2SO_4$ was dissolved in $x \ g$ of $H_2O$. The change in freezing point was found to be $3.82 \ ^oC$. If $Na_2SO_4$ is $81.5 \%$ ionised,the value of $x$ ($K_f$ for water $= 1.86 \ ^oC \ kg \ mol^{-1}$) is approximately .............. $g$ (molar mass of $S = 32 \ g \ mol^{-1}$ and that of $Na = 23 \ g \ mol^{-1}$)

The freezing point of a $0.2 \ m$ aqueous solution of a weak acid $(HX)$ which is $20\%$ ionized is ......... $^oC$. (Given: $K_f = 1.86 \ ^oC/m$ for water)