Actinium(III) oxide
Actinium oxide is a chemical compound containing the rare radioactive element actinium. It has the molecular formula Ac2O3. It is similar to its corresponding lanthanum compound, lanthanum(III) oxide, and contains actinium in the oxidation state +3. Actinium oxide is not to be confused with Ac2O, where Ac is an abbreviation for acetyl instead of the symbol of the element actinium.