Volume of ice increases when water converts into ice because of the unique structure of ice crystals.

Water molecules in the liquid state are more densely packed compared to the solid state of ice. When water freezes, the molecules arrange themselves in a hexagonal lattice structure, with each water molecule forming hydrogen bonds with its neighbouring molecules.

This arrangement creates open spaces between the molecules, leading to a less dense structure and a larger volume compared to liquid water. As a result, the volume of water increases when it converts into ice.