<P> Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as reducing agents, reductants, or reducers . The reductant (reducing agent) transfers electrons to another substance, and is thus itself oxidized . And, because it "donates" electrons, the reducing agent is also called an electron donor . Electron donors can also form charge transfer complexes with electron acceptors . </P> <P> Reductants in chemistry are very diverse . Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents . These metals donate or give away electrons readily . Hydride transfer reagents, such as NaBH and LiAlH, are widely used in organic chemistry, primarily in the reduction of carbonyl compounds to alcohols . Another method of reduction involves the use of hydrogen gas (H) with a palladium, platinum, or nickel catalyst . These catalytic reductions are used primarily in the reduction of carbon - carbon double or triple bonds . </P> <P> Each half - reaction has a standard electrode potential (E), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half - reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized: </P> <Dl> <Dd> ​ ⁄ H → H + e . </Dd> </Dl>

What is a redox reaction give an example