be in the same group. be in the same period. have nearly the same mass. have the same number of protons.
I gave my students this multiple choice question: Copper and gold have similar reactive properties. On the Periodic Table of the Elements, these elements are most likely to

Only one answer is correct among these 4 choices:
- be in the same group.
- be in the same period.
- have nearly the same mass.
- have the same number of protons.

Could you tell me which one is correct?

be in the same group.