$\mathrm{\Delta }{\mathrm{T}}_{\mathrm{f}}\propto \mathrm{m}\times \mathrm{i}$
m = morality, i = Vant Hoff factor
Except glucose, all other a electrolytes are undergoing dissociation so $(\mathrm{i}>1)$ . Glucose is non electrolyte, $\mathrm{i}=1$ . so it has least value of $\mathrm{\Delta }{\mathrm{T}}_{\mathrm{f}}$ hence its freezing point is maximum.