A reducing agent (also called a reductant or reducer) is the element or compound in a reduction-oxidation (redox) reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized". This means that there must be an "oxidizer"; because if any chemical is an electron donor (reducer), another must be an electron recipient (oxidizer). Thus reducers are "oxidized" and oxidizers are "reduced". The reducing agent in this reaction is ferrocyanide ([Fe(CN)₆]⁴⁻). It donates an electron, becoming oxidized to ferricyanide ([Fe(CN)₆]³⁻), simultaneously the oxidizer chlorine is reduced to chloride.

2 [Fe(CN)₆]^4- + Cl₂ → 2 [Fe(CN)₆]^3- + 2 Cl^-

Common reducing agents

aluminium hydride (LiAlH₄)
Nascent
amalgam
(NaBH₄)
Compounds containing the Sn²⁺ ion, such as tin(II) chloride
Sulfite compounds
(Wolff-Kishner reduction)
-mercury amalgam (Zn(Hg)) (Clemmensen reduction)
Diisobutylaluminum hydride (DIBAH)
Lindlar catalyst
(C₂H₂O₄)
(HCOOH)

Phosphites, hypophosphites and
() – used in biochemistry labs to avoid S-S bonds
Compounds containing the Fe²⁺ ion, such as iron(II) sulfate

Several common reducing agents and their products