Answer: Ice is less dense than water.
-------
This is a property of water, one that is crucial for ocean life because the ice keeps the entire ocean from freezing in very cold temperatures. If the ocean froze over, much of the life would not be able to survive.
Ice is less dense than water because of the hydrogen bonds. In solid form, the hydrogen bonds orient themselves in such a way that the molecules are further apart, lowering the density of ice.
