Which of the following experiments proved the existence of the nucleus? a) the photoelectric effect b) the Millikan oil-drop experiment c) the Rutherford scattering experiment d) the Stern-Gerlach experiment

These are the summaries of the given experiments: a) The photoelectric effect is a phenomenon where electrons are emitted from a material after the absorption of energy from electromagnetic radiation, typically in the form of visible or ultraviolet light. b) The Millikan oil-drop experiment measured the charge of an electron by observing and calculating the motion of tiny oil droplets in an electric field. c) The Rutherford scattering experiment consisted of firing alpha particles (helium nuclei) at a thin gold foil and measuring the distribution of the scattered particles. This experiment revealed the existence of a nucleus in an atom. d) The Stern-Gerlach experiment measured the deflection of single silver atoms subjected to an inhomogeneous magnetic field, demonstrating the quantization of angular momentum.

The experiment which provided evidence for the existence of the nucleus is the Rutherford scattering experiment (c). This experiment showed that the vast majority of the mass of an atom is concentrated in its center, which is now known as the nucleus.