Protons and neutrons are located in the nucleus of what?
Protons and neutrons are located in the nuclei of all atoms except hydrogen-1.
The nucleus contains all of the mass of the atom. Almost all of the mass of the atoms is made up of the protons and the neutrons.
The most common isotope of hydrogen has only one proton and no neutrons. This is the only nucleus of an atom that doesn't contain neutrons.