You can get the concept of: Law of Raoult's, cryoscopy, chemical potential, Gibbs-equation Gelmgoltsa, Factor Van Hoff.
Principle: The freezing point of solution is lower than the pure solvent. Lowering the freezing point can be determined experimentally, using a suitable apparatus (Cryoscopes). If we know the cryoscopic constant of the solvent, we can determine the molecular weight solutes.