Four aqueous solutions, each of molality $0.10\mathrm{mol}\mathrm{k}{\mathrm{g}}^{-1}$, are prepared. Assume that every electrolyte dissociates completely. Which solution has the highest freezing point?

Depression of freezing point is $\Delta T_f=i{K}_{f}m$, so the solution with the smallest number of particles per formula unit has the smallest depression and the highest freezing point. Glucose has $i=1$, while $\mathrm{NaCl}$, $\mathrm{CaCl}{}_2$ and $\mathrm{AlCl}{}_3$ have $i=2,3,4$. Hence glucose gives the highest freezing point.