Helium has
an atomic number of two.
The Big Bang Theory Season 7, Episode 3
You see, instead of
using liquid HELIUM...
The Big Bang Theory Season 11, Episode 8
Not quite accurate.
The Macy's balloons are filled with HELIUM...
The Big Bang Theory Season 4, Episode 24
You and Sheldon already came up
with your superfluid HELIUM model.
The Big Bang Theory Season 9, Episode 16