Why doesnt ice sink?

Answer 1

H2O is one of the few compounds on earth that expands when it freezes. This expansion causes ice to be less dense than water and causes it to float on the surface.

An unusual property of ice frozen at a pressure of one atmosphere is that the solid is some 8% less dense than liquid water. Water is the only known non-metallic substance to expand when it freezes. Ice has a density of 0.9167 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is most dense, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the temperature drops to 0 °C. (In fact, the word "crystal" derives from Greek word for frost.) This is due to hydrogen bonds forming between the water molecules, which line up molecules less efficiently (in terms of volume) when water is frozen. The result of this is that ice floats on liquid water, an important factor in Earth's climate. Density of ice increases slightly with decreasing temperature (density of ice at −180 °C (93 K) is 0.9340 g/cm³).

Answer 2

It doesn't sink because of density. If it is lighter than the material around it, then it will float. {And at first it might stick to the bottom.} The same goes for water vapor and air.