Helium/Melting point

-272.2 °C

Source = LANL

Helium is the only liquid that cannot be solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but will readily solidify by increasing the pressure. Helium-4 (⁴H) has a sharp transition temperature at 2.174K. Above this temperature it behaves as a normal liquid, but below it it expands on cooling, its conductivity for heat is enormous, and neither its heat conduction nor viscosity obeys normal rules.