a single, negatively-charged nucleus. equal numbers of protons and electrons. "shared" electrons from another atom. a stable number of charged neutrons.
I gave my students this multiple choice question: An atom will always have

Only one answer is correct among these 4 choices:
- a single, negatively-charged nucleus.
- equal numbers of protons and electrons.
- "shared" electrons from another atom.
- a stable number of charged neutrons.

Could you tell me which one is correct?

equal numbers of protons and electrons.