D. They showed that the atoms have a dense nucleus. Rutherford put Thomson's hypothesis to test by devising a "gold foil" experiment, he figured that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. If he shot high velocity alpha particles (helium nuclei) at an atom there would be very little to deflect the alpha particles. He tested this with a thin film of gold atoms, finding that most alpha particles went directly through the gold foil but, a few alpha particles rebounded backwards, which was not consistent with Thomson's model. He was forced to discard this model and reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an atom was concentrated in a nucleus.
