What do the elements He Ne Ar and Kr have in common?

The elements helium (He), neon (Ne), argon (Ar), and krypton (Kr) are all noble gases found in Group 18 of the Periodic Table. They are characterized by their full valence electron shells, which make them largely inert and nonreactive under normal conditions. Additionally, these gases are colorless, odorless, and monatomic, meaning they exist as single atoms rather than molecules. Their low boiling and melting points further distinguish them from other elements.