Reduction
The gain of electrons by a species, accompanied by a decrease in its oxidation number.
Formula / equation
Xⁿ⁺ + n e⁻ → X
Unit
Dimensionless
In depth
The name comes from the reduction in mass observed when a metal ore loses oxygen during smelting. Reduction always occurs at the cathode and consumes exactly the electrons released by the accompanying oxidation, so the two are inseparable.
Examples in the real world
Cu²⁺ + 2e⁻ → Cu plating out on an electrode; iron oxide reduced to iron in a blast furnace.