Final answer:
A neutral magnesium atom has 12 neutrons, which is calculated by subtracting its atomic number (12) from its atomic mass (24).
Step-by-step explanation:
The number of neutrons in an atom of Magnesium (Mg) can be determined by subtracting the atomic number from the atomic mass. Since Magnesium has an atomic number of 12 and an atomic mass of 24, we can calculate the number of neutrons as follows: Neutrons = Atomic Mass - Atomic Number = 24 - 12 = 12. Therefore, a neutral magnesium atom has 12 protons, 12 electrons, and 12 neutrons, making the correct answer (A) 12 neutrons.