Which term refers to the central part of an atom that is mainly comprised of protons and neutrons?

• A. Nucleus
• B. Electron
• C. Proton
• D. Neutron

Answer: (A)

This item tests knowledge of where the mass and positive charge of an atom are located. The central part of an atom, consisting mainly of protons and neutrons, is called the nucleus. Protons carry positive charge, neutrons have no charge, and together they form tightly bound nucleons held together by the strong nuclear force. This region contains most of the atom’s mass. Electrons, which are much lighter and negatively charged, orbit around this central region in electron shells or orbitals, kept near by the electromagnetic attraction to the positively charged nucleus. The nucleus is the correct term because it is the compact core that contains both protons and neutrons, unlike the surrounding electrons or the individual particles themselves.