Reduction is defined as which?

• A. Loss of electrons
• B. Gain of electrons
• C. Ion exchange
• D. Combustion

Answer: (B)

Redox chemistry centers on electron transfer. Reduction is the gain of electrons, which lowers the oxidation state of the element involved. A handy rule is OIL RIG: Oxidation Is Loss, Reduction Is Gain. So when a species gains electrons, it’s reduced. In soils, reduction happens under low-oxygen, waterlogged conditions as microbes donate electrons to reduced forms like Fe(III) or Mn(IV) oxides, turning them into Fe(II) or Mn(II) and often changing color and chemistry of the soil.

The other terms aren’t reductions: ion exchange is a separate mineral process involving swapping ions on surfaces, and combustion is burning that typically involves oxidation rather than reduction.