Who discovered the neutron?

The correct answer is Option D — James Chadwick. James Chadwick, a British physicist, discovered the neutron in 1932. The neutron is a neutral (no charge) subatomic particle found in the nucleus of atoms.

Why other options are wrong:

Option A (Ernest Rutherford): Rutherford proposed nuclear model and discovered proton existence, but NOT neutron.

Option B (Goldstein): Goldstein discovered canal rays (positive rays/protons) in 1886, NOT neutrons.

Option C (J.J. Thomson): Thomson discovered the electron in 1897, NOT neutron.