Question

Why is Ice less dense than water?

Answer 1

Intermolecular hydrogen bonding between the H₂O molecules at 0 ^oC becomes stable and stronger as water is cooled below 4 ^oC. And when the temperature of the water reaches 0 ^oC or below strong stable hydrogen bonds forms a rigid hexagonal crystal lattice structure. This is also called open cage structure between the water molecules. This makes water solid in form of ice and net space occupied by the molecules increases. Hence, density ice becomes less than that of water and it floats.