What happens to the density of water when it freezes to become ice?

Density of water decreases when it becomes ice.

Explanation:

Density of a quantity that relates a mass to the volume it occupies , this tells us that there is an inverse relationship between density and volume: as the volume that a mass occupies increases, its density decreases.

The density of water when moving from a liquid state to a solid (frozen) state decreases, because solid water occupies a larger volume.

And because objects with a lower density than liquid water tend to float, this is why ice cubes float.