Answer:
A.) 28
Explanation:
The mass number is the number of protons and neutrons within a particular atom. The charge of the atom is irrelevant because the mass number is not affected by the number of electrons.
Unless this atom is an isotope (different number of neutrons), there should be an equal amount of protons and neutrons.
As such, since the mass number is 56, there should be 28 protons and 28 neutrons (56 / 2 = 28).
