# What is the systematic name of Mg(NO_3)_2?

Magnesium is a group 2 alkaline earth metal, which forms a $2 +$ cation, $\text{Mg"^(2+)}$. Nitrate is a polyatomic anion which has a charge of $1 -$. Its formula is ${\text{NO"_3}}^{-}$.
Ionic compounds are named for the cation and anion present in the compound. Since $\text{Mg(NO"_3)_2}$ contains the cation magnesium and anion nitrate, its name is magnesium nitrate.
When naming an ionic compound with a polyatomic ionic, we don't use Greek prefixes to indicate the number of polyatomic ions. This is why the name of $\text{Mg(NO"_3)_2}$ is magnesium nitrate, and NOT magnesium dinitrate.