Which statement best describes the particles that reside in the atomic nucleus and contribute to its mass?

• A. Electrons
• B. Protons
• C. Neutrons
• D. Protons and Neutrons

Answer: (D)

The main idea is that the nucleus gets its mass from the nucleons inside it: protons and neutrons. These particles, collectively called nucleons, each have about the same mass, and the nucleus is made up of several of them. Electrons orbit around the nucleus in the electron cloud and have masses that are vastly smaller than those of protons and neutrons, and they do not reside in the nucleus. So the particles that live in the nucleus and mainly determine its mass are protons and neutrons.