Why is ice less dense than liquid water?

The answer is: Ice expands (volume is increasing) when it freezes, because of hydrogen bonds.

When molecule frezes, it lose energy. When molecules are far apart, it means the volume is greater and it expands.

For example, ice expands when water is freezing.

Hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (H), covalently bound to a highly electronegative atom such as flourine (F), oxygen (O) and nitrogen (N) atoms.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation: