Chadwick's discovery involved bombarding atoms with helium nuclei (alpha particles). Which option describes this experiment?

• A. Bombarding atoms with helium nuclei
• B. Charging electrons in a cathode ray
• C. Observing spectral lines
• D. Electrolysis

Answer: (A)

The main idea here is how neutrons were produced in Chadwick’s work: he used alpha particles, which are helium nuclei, to collide with atoms. Bombarding atoms with helium nuclei is exactly describing that setup, because the alpha particles act as high-energy probes that interact with the nucleus and reveal neutral particles—neutrons. Chadwick showed that this radiation was neutral and capable of knocking protons from other materials, confirming the existence of neutrons. The other descriptions point to different classic experiments—cathode rays reveal electrons, observing spectral lines relates to electron energy levels and emission spectra, and electrolysis is a chemical process—so they don’t describe Chadwick’s neutron discovery.