Answer:
Ice floats in liquid water because it is less dense than liquid water. This is because the hydrogen bonds that hold water molecules together in ice are more ordered and spaced farther apart than in liquid water. As a result, there is more empty space between the water molecules in ice than in liquid water, making ice less dense.
This is counterintuitive since most substances become denser as they solidify. However, water is different because of the way its molecules interact. Water molecules are polar, meaning they have a slight positive charge on one end and a slight negative charge on the other end. This allows them to form hydrogen bonds with each other, which are stronger than the van der Waals forces that hold most other substances together.
When water freezes, the hydrogen bonds between water molecules become more ordered and form a crystalline structure. This structure has empty spaces between the water molecules, which makes ice less dense than liquid water. Because ice is less dense than liquid water, it floats on top of it. This is important for aquatic ecosystems since if ice were denser than liquid water, it would sink and accumulate at the bottom of bodies of water, which could have negative effects on the organisms living there.