Standard Definitions of Reduction in Chemistry

Steps:

• Recall OIL RIG mnemonic: Oxidation Is Loss of electrons, Reduction Is Gain of electrons.
• For oxygen: reduction means loss of oxygen atoms from a compound, as in metal oxide to metal.
• For hydrogen: reduction means gain of hydrogen atoms, as in hydrogenation of unsaturated compounds.
• Match to options: loss of oxygen, gain of hydrogen, gain of electrons identifies D.

Why D is correct:

• Aligns with redox definitions: reduction = gain of electrons (e⁻), loss of O, or gain of H, per standard chemistry texts like those explaining MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O (Mn gains electrons, loses oxygen).

Why the others are wrong:

• A: Wrong on oxygen (gain instead of loss) and electrons (gain correct, but hydrogen loss is oxidation).
• B: Wrong on electrons (loss is oxidation, not reduction).
• C: Wrong on hydrogen (loss is oxidation) and electrons (loss is oxidation).

Final answer: D