CBSE Class 12-science Answered

When sodium chloride or NaCl dissolves in water, each molecule separates into sodium ions (Na⁺) and chloride ions (Cl^-), which mix separately among the water molecules. These ions affect the water molecules and their freezing point.

Water molecules form crystals when they freeze (ice). But when there is a salt in the water, the Na⁺ and Cl^- ions get in the way of the water molecules, making it more difficult for them to rearrange into crystals. Salt disrupts this equilibrium. It is a colligative property. The molecules of water use energy to exclude the sodium ions and chloride ions and thus freeze at lower temperatures.