Concept:Neutrons were discovered by James Chadwick in 1932.Explanation:Chadwick was a British physicist who identified the neutron, an uncharged subatomic particle.He received the 1935 Nobel Prize in Physics for this discovery.Ernest Rutherford proposed the nuclear atom and discovered alpha and beta rays.J.J. Thomson discovered the electron.John Dalton introduced the atomic theory.Therefore, the correct option is Chadwick.Answer:A. James Chadwick