Helium has
an atomic number of two.
The Big Bang Theory Season 7, Episode 3
Hey, in your super-cooled
HELIUM experiments,
The Big Bang Theory Season 9, Episode 16
Be even better if he swapped out
the HELIUM for xenon.
The Big Bang Theory Season 11, Episode 8
the abbreviation for HELIUM.
The Big Bang Theory Season 7, Episode 3