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(C) The depression in freezing point is given by $\Delta T_f = i 	imes K_f 	imes m$. The freezing point is $T_f = T_f^0 - \Delta T_f$. To have the h

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$0.2 \ m$ urea solution

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(C) The depression in freezing point is given by $\Delta T_f = i 	imes K_f 	imes m$. The freezing point is $T_f = T_f^0 - \Delta T_f$. To have the highest freezing point,the value of $\Delta T_f$ must be the lowest,which means the van't Hoff factor $(i)$ multiplied by molality $(m)$ must be the minimum.For $A$: $i = 3$ $(Ca^{2+} + 2NO_3^-)$,$i 	imes m = 3 	imes 0.12 = 0.36$.For $B$: $i = 2$ $(Na^+ + Cl^-)$,$i 	imes m = 2 	imes 0.15 = 0.30$.For $C$: $i = 1$ (urea is non-electrolyte),$i 	imes m = 1 	imes 0.2 = 0.20$.For $D$: $i \approx 1$ (weak acid,$CH_3COOH$ is slightly dissociated),$i 	imes m \approx 1 	imes 0.2 = 0.20$. Since $CH_3COOH$ dissociates slightly,$i > 1$,so $i 	imes m > 0.20$.Comparing the values,urea has the lowest $i 	imes m$ value,thus it has the highest freezing point.

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

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