# What is the formula for magnesium carbonate?

$M g C {O}_{3}$
Magnesium is an alkaline earth metal, and forms a $M {g}^{2 +}$ ion....
And carbonate ion, $C {O}_{3}^{2 -}$, has an equal an opposite charge. And thus the ionic species is $M g C {O}_{3}$.