Which scientist is credited with discovering the neutron?

• A. Rutherford
• B. Dalton
• C. Bohr
• D. James Chadwick

Answer: (D)

Understanding the neutron involves recognizing that the nucleus contains a neutral particle besides protons. The neutron is uncharged and has about the same mass as a proton, which helps explain why atoms can have different masses (isotopes) without changing charge.

James Chadwick clarified this by showing that neutral, massive particles were emitted from the nucleus. In his 1932 experiments, he bombarded beryllium with alpha particles and detected penetrating radiation that did not respond to electric or magnetic fields but could eject protons from other materials. This pointed to a new particle with no charge yet substantial mass—the neutron. Recognizing this particle completed the picture of the nucleus as made of protons and neutrons, helping explain nuclear stability and isotopes.

Rutherford had already revealed the existence of a nucleus but did not identify neutrons; Dalton proposed atomic theory long before neutrons were known; Bohr developed a model of electrons in quantized orbits, not neutrons. James Chadwick is the scientist credited with discovering the neutron.