If the freezing point of an aqueous 0.10 m glucose solution is −x°c, what is the approximate freezing point of a 0.10 m nacl solution?

Answer is: the approximate freezing point of a 0.10 m NaCl solution is -2x°C.
Van't Hoff factor (i) for NaCl solution is approximately 2.
Van't Hoff factor (i) for glucose solution is 1.
Change in freezing point from pure solvent to solution: ΔT = i · Kf · m.
Kf - molal freezing-point depression constant for water is 1,86°C/m.
m -  molality, moles of solute per kilogram of solvent.
Kf and molality for this two solutions are the same, but Van't Hoff factor for sodium chloride is twice bigger, so freezing point is twice bigger.