What is the charge of a magnesium ion?

Magnesium will remain positively charged + 2 → Mg⁺²

Explanation:

The octet rule states that the atoms of the elements bind each other in the attempt to complete their valence shell with eight electrons. That is to say, the atoms will tend to yield or share electrons to complete eight electrons in the valence layer through an ionic, covalent or metallic bond.

In other words, the objective is to have the closest noble gas electronic configuration, thus having the last complete electron layer and acquiring stability.

This defines the electronic tendencies of each atom, being able to yield (and we call these cations) or tendency to accept (and we call them anions).

In the case of Mg, this element is closer to Ne (Neon) and will tend to lose the last two electrons and thus, its electronic configuration would be the same. In this way, since electrons are negative, Magnesium, by transferring its electrons, will remain positively charged + 2 → Mg⁺²

2 + charge electrons of course