Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom?

Some uncharged particles are scattered by a gold foil.

All uncharged particles are attracted towards a gold foil.

All positively charged particles pass straight through a gold foil.

Some positively charged particles bounce back from a gold foil.

The Rutherford gold foil experiment explained or demonstrate that there is a small dense positively charged part in the center of atom.

In the experiment when alpha particles (2 protons and 2 neutrons, a positively charged particle) was bombarded on gold foil, some of these charged particles bounced back. They returned at 180 degrees.

As the alpha particles are positive and they bounced back it means they repelled by something of same kind of charge [like charges repel each other], this proof that there is positively charged center.

Some positively charged particles bounce back from a gold foil.

Explanation:

Observation made in Rutherford's gold foil experiment:

1. Most of the particles pass through the foil undeflected indicating that the atom is mostly empty space.

2. Some particles show a small angle f deviation indicating that the center of the atom has a positively charge nucleus.

3. Also some of the particles bounce off or deflect by 180 degree angle indicating that the mass of the atom lies in its center, and occupies a small volume.