The atomic number represents the number of protons in the nucleus of an atom. In this case, the atomic number is 12, which means the atom has 12 protons.
The mass number represents the total number of protons and neutrons in the nucleus of an atom. In this case, the mass number is 24. Since the atom is neutral, the number of electrons must be equal to the number of protons.
Therefore, the atom with an atomic number of 12 and a mass number of 24 contains 12 electrons.
