Explanation:

In chemistry and physics, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines an isotope's mass number. Until the 1960s, nucleons were thought to be elementary particles, not made up of smaller parts. A nucleon is either a proton or a neutron, considered in its role as a component of an atomic  nucleus.