# What is the oxidation number of manganese in "Mn"_2"O"_3 ?

$+ 3$
In oxides of elements, oxygen atoms normally have $\left(- 2\right)$ as the value.of the oxidation state.
That means $\left(- 6\right)$ charge comes from $3$ oxygen atoms. Since ${\text{Mn"_2"O}}_{3}$ is a neutral compound, each $\text{Mn}$ atom should have $\left(+ 3\right)$ oxidation value to balance the charge from the oxygen atoms.