Which of the following has the largest relative mass?

The proton has the largest relative mass among the options listed. Protons are one of the two types of particles that make up the nucleus of an atom, the other being neutrons. Protons have a relative mass of approximately 1 atomic mass unit (amu), which is significantly greater than that of electrons.

Electrons, in contrast, have a much smaller relative mass of about 1/1836 of a proton. While neutrons also have a relative mass close to that of protons (around 1 amu), the mass of a neutron is slightly greater than that of a proton; however, in many contexts regarding relative mass, protons are often recognized in discussions about atomic structure due to their positive charge and the way they impact the element's identity.

Thus, while both protons and neutrons are relatively large compared to electrons, the proton is conventionally considered to have the largest relative mass in contexts focused on atomic structure and behavior.