Explanation:

- James Chadwick (Option 3) is credited with the discovery of the neutron in 1932. He demonstrated that another particle in the nucleus had no charge, leading to a better understanding of atomic structure. Chadwick's work earned him the 1935 Nobel Prize in Physics.

- Enrico Fermi (Option 1) was an influential physicist known for his work on nuclear reactions and quantum theory, but not for discovering the neutron.

- J.S. Fleming (Option 2) was an electrical engineer and physicist, known for inventing the vacuum tube but not related to neutron discovery.

- Max Planck (Option 4) is known for founding quantum theory but was not involved in discovering the neutron.

.