Which one of the following compounds does not exhibit a different oxidation number of the same element?

In chemistry, mixed-valence compounds contain the same element in multiple oxidation states. Fe3O4 (magnetite) is a classic mixed-valence oxide consisting of FeO and Fe2O3, where iron exists as both Fe2+ and Fe3+. Similarly, Mn3O4 (hausmannite) is a mixed-valence oxide containing Mn2+ and Mn3+ ions [1]. Pb3O4 (red lead) is another example, composed of Pb2+ and Pb4+. In contrast, Fe2O3 (hematite) is a simple oxide where all iron atoms exhibit a single oxidation state of +3 to balance the -2 charge of the three oxygen atoms. While the question lists Pb2O4, it is likely a typographical error for the common mixed-valence oxide Pb3O4; however, Fe2O3 remains the only compound in the list that strictly represents a single oxidation state (+3) for the metal cation.

Sources

1. [1] https://www.sciencedirect.com/science/article/pii/S2772571523000153