Answer: the last option, positive charge occupies a very small volume in the atom.
Explanation:
1) Earlier, JJ Thomson demonstrated that the electrons were subatomic particles and proposed the plum pudding model, in which the electrons are embedded in a positve mass. This model did not explain a lot of facts and was soon replaced.
2) Ernest Rutherford's experiments demonstrated the existence of the atomic nucleus: a tiny region with most of the mass of the atom and the positive charge.
3) Rutherford came up with this conclusion after the amazing results of the gold foil experiment which showed that some α particles (helium nucleii, which have positive charge) bounced off instead of pass through or being slighted deflected.
The bouncing of the α partilces, was infered to be the result of the repulsion by massive positive charge concentrated in small regions, this is the nucleus of the atom.
