Which particle is represented by the plums in plum pudding model (Or chips chocolate chip cookie model)?

The plums in the plum pudding model represent electrons. In this model, the atom is envisioned as a positively charged sphere (the "pudding") with negatively charged electrons (the "plums") embedded within it. This model was proposed by J.J. Thomson in 1904 and was the dominant model of atomic structure until the Rutherford scattering experiment in 1911 showed that the positive charge of the atom was concentrated in a very small nucleus, with the electrons orbiting around it.