In which of the following compounds does oxygen have an oxidation number other than -2?

• A. CO2
• B. H2O
• C. H2O2
• D. SO2

Answer: (C)

Verified step by step guidance

1. Recall that the common oxidation number of oxygen in most compounds is -2, but there are exceptions such as peroxides and superoxides.
2. Analyze each compound to determine the oxidation state of oxygen by using the known oxidation states of other elements and the overall charge balance of the molecule.
3. For CO2: Carbon typically has an oxidation state of +4, and since the molecule is neutral, oxygen must be -2 to balance the charge.
4. For H2O: Hydrogen has an oxidation state of +1, so oxygen must be -2 to balance the two hydrogens in the neutral molecule.
5. For H2O2 (hydrogen peroxide): Hydrogen is +1, but oxygen atoms are bonded together, which changes their oxidation state to -1 each, differing from the usual -2.