Helium (He), chemical element, inert gas of Group 18 (noble gases) of the periodic table.
The second lightest element (only hydrogen is lighter), helium is a colourless, odourless,
and tasteless gas that becomes liquid at −268.9 °C (−452 °F). The boiling and freezing points
of helium are lower than those of any other known substance. Helium is the only element that
cannot be solidified by sufficient cooling at normal atmospheric pressure; it is necessary to
apply pressure of 25 atmospheres at a temperature of 1 K (−272 °C, or −458 °F) to convert it
to its solid form.