Looking at the molecular formula of Cr₂O₃, we know that oxygen has an oxidation state of -2, and three oxygen atoms means they are providing a total charge of -6 to the species. Since the compound is charge-neutral overall, the two chromium atoms must have a total charge of +6 to balance the -6; therefore, each chromium atom must have a charge of +3. This means that the chromium atoms in this molecule are Cr³⁺. To name this compound we will refer to the metal as chromium(III), to give a full name of chromium(III) oxide.
Since chromium can have multiple oxidation states, such as Cr²⁺ or Cr⁴⁺, it is a Type II ion.
