electrons in the outer shell. neutrons in the outer shell. electrons in the nucleus. protons in the nucleus.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: The atomic number of an element refers to the number of
Possibilities:
- electrons in the outer shell.
- neutrons in the outer shell.
- electrons in the nucleus.
- protons in the nucleus.

protons in the nucleus.