Answer
Electrons
Protons
Plum Pudding Model, Bohr Model, Modern Atomic Model
Work Step by Step
Thomson primarily studied and discovered the electron. In fact, the proton and neutron were not yet discovered. In fact, Thomson supposed the electrons were held within positively-charged materials in his Plum-Pudding Model. Therefore, he would support the electron as the most important for formation of compounds.
Thomson would then propose the proton or positively-charged material as he included a positively-charged material with his Plum-Pudding model. Neutrons had not been discovered by the time of his Plum-Pudding Model.
The Plum Pudding Model, Bohr Model, and Modern Atomic Model fit with Thomson's findings as he showed that every atom contains electrons which each of these models share.
