# What is the oxidation number of MnO2?

The oxidation number of $\text{MnO"_2}$ is $0$.
The sum of the oxidation numbers of the elements In a neutral compound is $0$.
The oxidation number of the oxide anion is $\text{-2}$. Since there are 2 oxide ions, the total oxidation number for the oxide is $\text{-4}$. Since the sum of the oxidation numbers must be $0$, the oxidation number of the manganese cation is $\text{+4}$. Therefore, $\text{MnO"_2}$ is the ionic compound manganese(IV) oxide.