We’re being asked to determine the solution will have the lowest freezing point.
Recall that the freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔTf) is given by:
The change in freezing point is also related to the molality of the solution:
i = van’t Hoff factor
m = molality of the solution (in m or mol/kg)
Kf = freezing point depression constant (in ˚C/m)
The solution with the highest change in freezing point (ΔTf) will be the solution with the lowest freezing point.