• A redox reaction must involve a change in oxidation number for two of the elements involved in the reaction.
  • The oxidized element increases in oxidation numbers, while the reduced element decreases.
  • Most combination and decomposition reactions are redox reactions since elements are usually transformed into compounds and vice-versa.
  • Double-replacement reactions are not redox because ions are simply recombined without any transfer of electrons.
  • Acid-base reactions, like the one below, are also notRedox reactions.
  • Any reaction in which no oxidation numbers change is not a Redox reaction.
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