are in the same period. are in the same family. have the same number of electrons. have the same atomic mass number.
I gave my students this multiple choice question: Certain elements with similar chemical and physical properties are found in the same column in the Periodic Table of the Elements. These chemicals

Only one answer is correct among these 4 choices:
- are in the same period.
- are in the same family.
- have the same number of electrons.
- have the same atomic mass number.

Could you tell me which one is correct?

are in the same family.