Question

What happens to the density of water when it is heated above $4°C$?

Answer 1

The density of a substance decreases with an increase in temperature if the substance expands on heating.
But water is an exception to this. The density of water increases from $0°C\mathrm{to}4°C$and then decreases when heated above $4°C$.
Therefore, in this case when water is heated above$4°C$, it's density decreases. It has maximum density at $4°C$