Question

During the winter months, water on the surface of a pond will typically freeze and this ice acts as an insulator for the water beneath it. As a result, aquatic life is able to survive during the cold winter. The reason that this water expands upon freezing is due to

Answer 1

Hydrogen bonding allows the water to expand

Answer 2

when the water freezes, its molecules are perfectly ordered and separated from each other at the same distance. This generates, that in the ice there are less water molecules in a certain volume, that is, they occupy more space.

The ice (frozen water) when expanding, causes its density to become lower than in a liquid state. For this reason the ice floats in the water and allows life under frozen lakes.