The answer should be C, most of the mass of the atom is located in the nucleus.
First, we need to know that an atom includes mainly 3 subatomic particles, which are proton, neutron, and electron. Proton and neutron are located in the nucleus of the atom, while electrons are moving freely outside the nucleus. Each proton carries a positive charge, neutron has no charge, and each electron carries a negative charge.
A is not correct because the nucleus only takes a small space from the atom, instead, the area for the electrons takes up the most space.
B is not correct because only proton locates in the nucleus, and the charge of the atom is also determined by the number of electrons outside of the atom.
And c is correct because protons and neutrons are the heaviest, while electrons are so light that sometimes we can neglect their weight.
Therefore, your answer should be C.
