Neutral atoms have the same number of protons as electrons. what would make the electrically charged magnesium ion, mg2+, neutral?

Mg2+ is the positive ion of the neutral atom Mg. This means that the neutral atom Mg lost the two excess electrons in its outermost energy level and became a positive ion with the two excess positive charges. To become neutral again, the Mg2+ ion has to regain two electrons again to balance the negative charge with the excess two positive charges.

Nonmetals usually react by gaining electrons