Question

what is the atomic number?* the number of protons in the nucleus the number of protons and neutrons in the nucleus the number of neutrons in the nucleus the number of protons in the energy levels outside the nucleus

Explanation:

Atomic number is defined as the number of protons in the nucleus of an atom. The number of protons and neutrons in the nucleus is the mass number. The number of neutrons alone is not the atomic number. Protons are in the nucleus, not in energy levels outside the nucleus.

Answer:

the number of protons in the nucleus