The correct answer is option c, that is, nucleus.
A usual atom comprises three subatomic particles, that is, the neutrons, protons, and electrons. According to Bohr's model, the majority of the mass of an atom is in the nucleus, that is, a small, dense region at the center of each atom, comprising nucleons.
The nucleons incorporate neutrons and protons. All the positive charge of an atom is found in the nucleus and arises from the protons, the neutrons are neutrally-charged, and the electrons are the negatively charged particles found outside of the nucleus.
