For 10 points, name this gas with atomic number two.
An ion containing this element along with fluorine and oxygen has been predicted stable. In one experiment, the nuclei of this element were fired at a thin layer of gold atoms. Superfluidity has been observed in both its isotopes three and four. This element is the lightest with a full s subshell. Its nuclei are alpha particles. For 10 points, name this gas with atomic number two.
An ion containing this element along with fluorine and oxygen has been predicted stable.
{helium} [or {He}]