Name an element of group 18 which can form compounds.

Helium (He) is an element in Group 18 of the periodic table, also known as the noble gases. While helium is typically inert and does not readily form compounds under normal conditions, there have been some experimental studies indicating that under extreme conditions, such as high pressure and low temperature, helium can form compounds, albeit very unstable ones. Examples include helium compounds like helium hydride (HeH+) and helium difluoride (HeF2), which have been synthesized under laboratory conditions. However, these compounds are highly reactive and short-lived.