An iron nail sinks in water but it floats in mercury. Why ?

Expain why, a piece of glass sinks in water but it floats in mercury.

A piece of nail sinks in water but a boat floats in it because

Steel sinks in water but a steel boat floats .why ?

While performing experiments with water, Jyoti observed that an empty steel bowl floats but a small iron nail sinks in water. This can be explained by the fact that