1. An atom is mostly empty space with a dense positively charged nucleus

Rutherford fired alpha particles at a piece of gold foil.  When he looked at the beams on a fluorescent screen, he noticed that most of the particles went straight through the foil and hit the screen because gold atoms were mostly empty space. Rutherford hypothesized that the small dense positively charged nucleus of the atom deflected a small percentage of the atoms.

Incorrect answers:

2. An atom is composed of at least three types of subatomic particles

B is not correct because Rutherford and his colleagues didn’t discover the third subatomic particle until a later experiment with nitrogen and alpha particles.

3. An electron has a positive charge and is located inside the nucleus

C is not correct because an electron has a negative charge and is not located inside of the nucleus.

4. An electron has the properties of both waves and particles

D is not correct because it is a conclusion of Young’s Quantum Mechanics.