Which reactions are oxidation-reduction reactions? Check all that apply.

A redox reaction involves changes in oxidation numbers. In choice C, carbon changes from an average oxidation number of −2 in C3H6 to +4 in CO2, while oxygen changes from 0 in O2 to −2 in the products. In choice D, iron changes from +3 in Fe2O3 to 0 as Fe, and carbon changes from +2 in CO to +4 in CO2. The oxidation numbers do not change in A or B, so those are not redox reactions.

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