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
