Answer:The correct answer is 'nucleons'.
Explanation;
An atom is a structural unit of matter.It consist of three subatomic particles: electrons, protons, and neutrons.
Protons and neutrons are located at center of an atom where whole mass of an atom is concentrated that is in the nucleus of a atom.
Protons and neutron being located in nucleus are also known as nucleons.
Where as electrons revolve around the nucleus in different orbits inside an atom.
Hence, the correct answer is 'nucleons'.