What characteristic of helium distinguishes helium from the other noble gases?

The characteristic that helium has that distinguishes it from the noble gases would be that it only has 2 valence electrons while noble gases has a completely filled orbitals giving it 8 valence electrons and a stable electron configuration. The valence electrons is the number of electrons that is present in an atom that can take part in the formation of bonds. These electrons can be found on the outermost shell of an atom. Helium is an exception to the octet rule, its atom has only two available electrons in its outermost shell since it only has one eletron shell that is the only the s orbital which can hold two electrons only.