Question

what did thomson contribute to the model of the atom?
the neutron
the nucleus
the electron
the electron cloud

Explanation:

J. J. Thomson discovered the electron in 1897 through cathode - ray tube experiments. He proposed the plum - pudding model of the atom where electrons were embedded in a positively charged sphere. The neutron was discovered by Chadwick, the nucleus was identified by Rutherford, and the concept of the electron cloud came later in the development of quantum mechanics.

Answer:

the electron