Here's why:

* Melting Point: -38.83 °C (-37.89 °F)

* Boiling Point: 356.73 °C (674.11 °F)

This means mercury remains a liquid from a very low temperature to a relatively high temperature, covering a range of over 395°C (743°F).

While other elements have higher boiling points, none have such a large difference between their melting and boiling points, making mercury unique in its liquid state range.