What subatomic particles are found in the nucleus of an atom?

The nucleus of an atom contains protons and neutrons, which are both classified as nucleons. Protons have a positive charge, while neutrons are neutral and carry no charge. This arrangement in the nucleus is crucial because it helps determine the atom's identity, mass, and stability.

Electrons, while they are subatomic particles associated with atoms, reside outside the nucleus in electron shells. They are responsible for chemical bonding and reactions, but they do not contribute to the mass of the nucleus itself.

The other choices mention particles that do not belong in the nucleus. Ions and anions refer to charged species formed by the loss or gain of electrons, while cations are positively charged ions, neither of which are subatomic particles found within the nucleus. Thus, the correct identification of protons and neutrons as the constituents of the atomic nucleus underscores their importance in defining the structure of matter at the atomic level.