Question 8
When a magnesium atom becomes an Mg2+ ion, what happens to the number of protons in its nucleus?
The right answer is the one marked above.
The proton count does not change. Only electrons move when an ion forms. Magnesium loses two electrons, and the +2 charge comes from having two more protons than electrons.
If the proton count changed, the particle would no longer be magnesium at all — the number of protons is what identifies an element. Nothing in chemistry alters the nucleus.