atomic mass negative electrical charge number of neutrons full valence electron shells
I gave my students this multiple choice question: Neon (Ne), argon (Ar), and krypton (Kr) are in the same column on the Periodic Table of the Elements. What characteristic do these elements have in common?

Only one answer is correct among these 4 choices:
- atomic mass
- negative electrical charge
- number of neutrons
- full valence electron shells

Could you tell me which one is correct?

full valence electron shells