# Question #d16a3

$M {g}_{3} {\left(P {O}_{4}\right)}_{2}$
Magnesium is in the group 2 of the periodic table that means that it's number of oxidation is 2+. Phosphate formula is $P {O}_{4}^{3 -}$, also we can see in the lewis structure that it has a charge of 3-.
So to balance the charges Mg +2, and $P {O}_{4}$ -3, the easiest way is to multiply between them, that is $+ 2 \cdot 3 = + 6$, and $- 3 \cdot 2 = - 6$, and now the charges are equal. Meaning you need 3 atoms of $M {g}^{2 +}$ and 2 molecules of $P {O}_{4}^{3 -}$, for charges to be equal.