What defines a baryon in particle physics?

A baryon is defined as a subatomic particle that is composed of three quarks. This characteristic distinguishes baryons from other classes of particles, such as mesons, which are made up of a quark and an antiquark. Baryons also belong to a category known as hadrons, which interact via the strong nuclear force. The most common examples of baryons are protons and neutrons, which are the constituents of atomic nuclei.

When considering the other options, a particle made up of two quarks refers to mesons rather than baryons. The definition of baryons explicitly includes their formation from three quarks. Similarly, while baryons are indeed influenced by the strong nuclear force, the claim that a baryon is not affected by this force does not align with the recognized properties of baryons. Lastly, baryons cannot simply be described as particles that can be split into protons and neutrons; rather, protons and neutrons themselves are baryons, consisting of three quarks each. Thus, option C accurately captures the defining aspect of baryons in particle physics.