And are located in the nucleus of the atom, while exist in orbitals in the empty space outside of the nucleus.

The atomic structure of an atom is well explained experimentally by different experiments like Rutherford's experiment etc

Based on these experiments it was determined that the atoms contains a central part known as nucleus which contains the positively charged sub atomic particles protons and neutral sub atomic particles neutron.

There is empty space around the nucleus in which negatively charged subatomic particles are found known as electrons.

So answers are

a) protons

b) neutrons

c) electrons

56 moles of   lieter in chemistry