Final answer:
Neutrons have the greatest mass among the given particles, followed closely by protons. Photons have no mass.
Step-by-step explanation:
The group of particles that has the greatest mass are the neutrons, which are slightly more massive than protons. Both protons and neutrons are much more massive than electrons. However, photons, the particles of light, have no mass.
Particle mass refers to the mass of an elementary particle, which is a fundamental particle that cannot be broken down into smaller constituents. In the context of particle physics, elementary particles are the basic building blocks of matter. These particles include quarks, leptons, and force carriers.