Question

Cacl2 is preferred to nacl for clearing snow on roads particularly in very cold countries . this is because

Answer 1

The freezing point drops when a non volatile solute is added to a solvent.
Depression in freezing point is directly proportional to the number of ions into which the salt dissociates, and can be calculated using the formula ΔT = Kf×b×i. (Kf is cryogenic constant, b is solvent molality
CaCl₂, upon dissociation, would give 3 ions, 2 Cl⁻ ions, and 1 Ca²⁺. NaCl on the other hand would just give 1 Cl⁻ and 1 Na⁺ ion on dissociation.
Hence, depression in freezing point in case of CaCl₂ would be more than that in case of NaCl since i for it is 3 and that for NaCl is 2. This is why CaCl₂ is preferred over NaCl.