Why is most of the mass of the atom in the nucleus?
A.Protons are located in the nucleus of the atom, and they are responsible for the mass of the atom.
B.Protons and electrons are located in the nucleus of the atom, and they are responsible for the mass of the atom.
C.Neutrons are located in the nucleus of the atom, and they are responsible for the mass of the atom.
D.Protons and neutrons are located in the nucleus of the atom, and they are responsible for the mass of the atom.