Step-by-step explanation:
It is known that an atom consists of three sub-atomic particles, that is, protons, neutrons, and electrons.
Protons and neutrons are located inside the nucleus of the atom whereas electrons revolve around the nucleus of the atom forming a cloud of electrons.
These electrons occupy orbits of their respective energy levels.
Therefore, we can conclude that electrons are modeled using a "cloud" around the nucleus because they revolve around the nucleus.