The correct answer is all the protons and neutrons (option b).
Explanation: In an atom, the nucleus is the dense central part that contains protons and neutrons. Protons are positively charged particles, while neutrons have no charge. Electrons, which are negatively charged, are found in orbitals around the nucleus rather than inside it. Therefore, while an atom is neutral overall with equal numbers of protons and electrons, the nucleus itself is composed solely of protons and neutrons.