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Which change identifies a reaction as an oxidation-reduction reaction?
AA solid product separates from the solution
BA hydrogen ion moves between two reactants
COne or more elements change oxidation number
DThe total mass of the products goes down
Answer & Solution
Correct answer: C. One or more elements change oxidation number
1. Work out the oxidation number of every element on both sides.
2. If at least one element changes value, the reaction is redox.
3. An increase is oxidation and a decrease is reduction.
4. Forming a solid marks precipitation, and moving H+ marks an acid-base reaction.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.2 Classifying Chemical Reactions_
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