Concept: The nucleus of an atom is the dense, central core that holds nearly all of the atom’s mass.Explanation: The nucleus contains two types of subatomic particles: protons and neutrons.Protons are positively charged, while neutrons have no charge. Together, they are called nucleons.Electrons are negatively charged and they orbit around the nucleus, so they are not part of the nucleus itself.Therefore, the correct description of the atomic nucleus is protons and neutrons.Answer: C. Protons and neutrons