The correct answer is Rutherford's gold experiment.
Rutherford’s gold foil experiment- It measured the scattering of an alpha particle beam when it strikes a thin metal foil - the discovery of Nucleus.
J.J. Thomson’s experiment - Cathode-ray tubes - showed that all atoms contain tiny negatively charged subatomic particles - the discovery of electrons.
Chadwick’s experiment - bombarded Beryllium with alpha particles from the natural radioactive decay of Polonium. - discovered the neutron
Millikan’s oil drop experiment - the charge of an electron was determined.