Answer:
The answer to your question is: B. 2
Explanation:
Magnesium is located in group IIA, that means that it has 2 electrons in its outermost shell, and these are the electrons that it can lose to become stable.
Oxygen is located in group VI A, that means that it has 6 electrons in its outermost shell and needs to electrons to become stable.
Mg⁺² + O₂²⁻ ⇒ MgO
