What particles are found in the nucleus of an atom?

The nucleus of an atom is comprised of protons and neutrons. Protons are positively charged particles that determine the atomic number of an element and, therefore, its identity. Neutrons, on the other hand, are neutral particles that contribute to the overall mass of the atom but do not affect its charge. Together, protons and neutrons make up the bulk of an atom's mass and are bound together in the nucleus by the strong nuclear force.

Electrons, although present in an atom, are found in the surrounding electron cloud and not in the nucleus. Positrons are not typically found in stable atoms as they are the antimatter counterparts of electrons and do not form a part of the atomic structure under normal circumstances. Thus, the correct answer identifies the two primary particles that reside within the nucleus, accurately reflecting the structure of an atom.