Ice floats in water because the solid form of water is lighter; it means the ice is less dense than the liquid form. This is unusual because in other substances it is just the other way round. Initially, water behaves like other substances. When it is heated, it expands and evaporates. When it is cooled, its volume becomes smaller. After a certain temperature, however, water becomes ‘wayward’. At 4°C, it reaches its densest state. On further cooling, it expands again! Thus, water behaves abnormally. This is also known as anomaly of water. On freezing, i.e., at 0°C, its volume increases again. This is the reason why water bottles full of water burst if they are kept in deep freezer for a long time.
