Which noble gas has the lowest atomic number?

The story behind the answer

Helium has the lowest atomic number (2) among the noble gases; neon is 10, argon 18, and krypton 36. Atomic number equals the number of protons, and it increases as you move down Group 18. Helium’s 1s2 configuration gives it a full outer shell, so it’s inert like the others.

Noble gases are grouped for their lack of reactivity due to complete valence shells. Though helium’s electrons fill an s orbital (others end in p), its behavior matches. Memory tip: learn the order He, Ne, Ar, Kr, Xe, Rn, Og—start with He to remember it has the smallest atomic number.