Explanation:
Charges on both magnesium and oxygen is 2. Though opposite in sign, they have equal charges so, both of them will be cancelled by each other.
As a result, formula of magnesium oxide is MgO and not [tex]MgO_{2}[/tex].
The student write the equation as [tex]Mg + O_2 \rightarrow MgO_2[/tex], it is not correct.
Therefore, given equation will be balanced as follows.
[tex]2Mg + O_{2} \rightarrow 2MgO[/tex]
Since, number of atoms on both reactant and product side are equal. Hence, this equation is completely balanced.
