The three subatomic particles are protons, neutrons, and electrons. Among these, the electron has the smallest mass.
Protons and neutrons are found in the nucleus of an atom and have similar masses. A proton has a mass of approximately 1.6726 x 10-27 kilograms, while a neutron has a slightly larger mass of about 1.6749 x 10-27 kilograms.
In contrast, an electron has a much smaller mass of about 9.1094 x 10-31 kilograms. This means that the mass of an electron is roughly 1/1836 times the mass of a proton or neutron.
Therefore, the electron is the subatomic particle with the smallest mass.