The energy levels of an atom are occupied by
a. electrons
c. neutrons
b. protons
d. ions

A

Explanation:

Electrons: This is the correct answer because electrons are the particles that spin around the atom, in a stable orbit. This orbit is known as an energy level. When an electron gets more energy, it may move to a higher energy level, and when it loses some energy, it may move to a lower energy level.

Protons: This is not the answer, because protons are positively charged particles that exist in the nucleus of the atom.

Neutrons: Like protons, these particles are also found in the nucleus of the atom. They are different from protons because they carry no charge.

Ions: Ions are charged atoms, and by this reason they cannot exist in an orbital level. For example, a sodium ion, is a positively charged version of the regular sodium atom. Hence, an atom cannot occupy the space of an orbital level. Another analogy that can be used is like saying that a house can occupy the space of a window.