Which particles can only be found in the nucleus of an atom?

• A. Electrons
• B. Protons and neutrons
• C. Photons
• D. Quarks

Answer: (B)

The nucleus houses the particles that make up most of an atom’s mass and electric charge, bound together by the strong force. Within this compact center reside protons, which carry positive charge, and neutrons, which are neutral. Electrons sit outside the nucleus in electron orbitals, attracted to the nucleus but not part of it. Photons are particles of light and are not constituents of the atom’s structure at all. Quarks are the smaller building blocks inside protons and neutrons, so they exist inside those nucleons rather than as separate, standalone particles in the nucleus. So, the particles found only in the nucleus are protons and neutrons.