sulfur (S) argon (Ar) fluorine (F) bromine (Br)
I gave my students this multiple choice question: An atom of which element contains one more proton than one atom of chlorine (Cl)?

Only one answer is correct among these 4 choices:
- sulfur (S)
- argon (Ar)
- fluorine (F)
- bromine (Br)

Could you tell me which one is correct?

argon (Ar)