Protons and neutrons present in the nucleus.
Explanation
The structure of an atom is divided into two primary regions: the central nucleus and the extra-nuclear region. The nucleus is the dense, central part of the atom that contains almost all of its mass.
The term "Nucleon" is the collective designation for the subatomic particles located within the atomic nucleus. Since the nucleus consists of protons and neutrons, these two particles are collectively known as nucleons.
- Protons: Positively charged particles residing in the nucleus.
- Neutrons: Electrically neutral particles residing in the nucleus.
- Electrons: Negatively charged particles present in the extra-nuclear region (orbitals); they are not classified as nucleons.
Key Takeaway
Nucleons refer exclusively to the particles present inside the nucleus, namely protons and neutrons. The sum of nucleons gives the mass number of the atom.