Which statement describes a concept included in the wave-mechanical model of the atom?

Below are the choices that can be found elsewhere:

(1) Positrons are located in shells outside the nucleus.

(2) Neutrons are located in shells outside the nucleus.

(3) Protons are located in orbitals outside the nucleus.

(4) Electrons are located in orbitals outside the nucleus.

The answer is 4 which is " Electrons are located in orbitals outside the nucleus."