The correct option is Option D: helium nuclei, which impinged on a metal foil and got scattered.

Rutherford's experiment is a landmark in the study of atomic structure. In this experiment, a beam of alpha particles, which are essentially helium nuclei (comprising two protons and two neutrons, and thus positively charged), was directed at a thin gold foil. Most of the alpha particles passed through the foil with little to no deflection, which suggested that atoms are mostly empty space. However, a small fraction of the alpha particles were deflected at large angles, and a very few even bounced back towards the source. This observation was unexpected based on the prevailing model of the atom at the time, which was J.J. Thomson's "plum pudding" model where the atom was thought to be a uniform sphere of positive charge with electrons embedded within it.

The results of Rutherford's experiment led him to propose a new model of the atom, known as the nuclear model. In this model, an atom consists of a small, dense nucleus that contains most of the atom's mass and all of its positive charge, surrounded by electrons that occupy the remaining vast space of the atom. The nucleus is tiny compared to the overall size of the atom, explaining why most alpha particles passed through the foil unimpeded. The large deflections occurred when an alpha particle came close to the nucleus, being repelled by its positive charge. This discovery was fundamental in moving away from the idea of an atom as a homogenous sphere to an atom with a dense central nucleus around which electrons orbit.