A cryoscopic constant is described as the freezing point depression when a mole of non-volatile solute is dissolved in one kg of solvent. The cryoscopic constant is denoted by kf. Freezing point depression refers to the lowering of the freezing point of solvents upon the addition of solutes. It is a colligative property described by the following formula.
ΔTf = i × Kf× m
Its unit is k.kg.mol−1. It depends on the molar mass of the solute in the solution.