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Which statement about the oxidation number of oxygen follows the assignment guidelines?
AIt is minus two normally and minus one in peroxides
BIt is minus one normally and minus two in peroxides
CIt is minus two in absolutely every compound formed
DIt is always positive when combined with any halogen
Answer & Solution
Correct answer: A. It is minus two normally and minus one in peroxides
1. Oxygen is assigned -2 in most compounds.
2. In peroxides it is -1, and in superoxides it is very rarely one half of minus one.
3. Positive values appear only when oxygen is combined with fluorine.
4. So the general value is -2 with -1 reserved for peroxides.
5. Claiming -2 in every compound would misread hydrogen peroxide entirely.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.2 Classifying Chemical Reactions_
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