According to the OIL RIG mnemonic, which statement is true?

• A. Loss of electrons
• B. Gain of electrons
• C. Change in oxidation number
• D. Transfer of protons

Answer: (D)

Redox processes revolve around electrons moving between species, which changes the oxidation state of the atoms involved. OIL RIG helps you remember that oxidation is the loss of electrons and reduction is the gain of electrons, and both of these are inherently linked to a change in oxidation number. Therefore, the statement that there is a change in oxidation number is the most general and defining truth for redox reactions. The idea of losing or gaining electrons is specific to one half of the process, and transfer of protons isn’t what defines redox—proton moves can occur in other contexts and don’t by themselves indicate oxidation or reduction.