The atom has 20 protons. The atom has 20 neutrons. The sum of the number of protons and electrons is 20. The sum of the number of protons and neutrons is 20.
I gave my students this multiple choice question: Which statement best describes an atom with an atomic number of 20?

Only one answer is correct among these 4 choices:
- The atom has 20 protons.
- The atom has 20 neutrons.
- The sum of the number of protons and electrons is 20.
- The sum of the number of protons and neutrons is 20.

Could you tell me which one is correct?

The atom has 20 protons.