Which experiment led to the understanding of the nuclear model of the atom?

The Geiger-Marsden experiment, also known as the Rutherford gold foil experiment, was pivotal in establishing the nuclear model of the atom. Conducted in 1909 by Hans Geiger and Ernest Marsden under the direction of Ernest Rutherford, the experiment involved firing alpha particles at a thin foil of gold.

The observation that some alpha particles were deflected at large angles, and a small fraction even bounced back, was unexpected based on the existing plum pudding model, which suggested that atoms were uniform and diffuse. The significant deflections indicated that a small, dense, positively charged nucleus must be present within the atom, leading to the conclusion that the atom consists of a central nucleus surrounded by electrons in orbit. This fundamentally transformed the understanding of atomic structure, establishing the basis for the nuclear model that describes atoms having a concentrated nucleus.

In contrast, the other experiments mentioned focused on different aspects of atomic physics. Millikan's oil drop experiment determined the charge of the electron, Thomson's cathode ray experiment identified the electron and proposed the existence of particles smaller than atoms, while Einstein's work on the photoelectric effect provided support for the quantum theory of light, but none of these directly contributed to the realization of the nuclear structure of the atom.