Reduction
Reduction is the gain of electrons or a fall in the oxidation state by a atom, molecule, or ion. Substances which have the ability to reduce the other substances are said to be reductive and are called as reductants, reducing agents, or reducers. This means that, the reductant transfers electrons to the other substance, and is hence itself oxidized. And, as it donates electrons, it is also known as electron donor. Electron donors can also form charge transfer complexes with the electron acceptors. Reductants in chemistry are quite diverse. Electropositive elemental metals, like lithium, zinc, sodium, magnesium, iron, aluminium, carbon, are good reducing agents. These metals donate or give away electrons easily. Hydride transfer reagents, like NaBH4 and LiAlH4, are extensively used in organic chemistry, primarily in reduction of carbonyl compounds to alcohols. Another method of the reduction involves the use of hydrogen gas (H2) with a platinum, palladium, or nickel catalyst. These catalytic reductions are used primarily in reduction of carbon-carbon double or triple bonds.
The reduction of a chemical species results in the gain of electrons for those species. This does not essentially include any change in charge, any time the atom increases its electron density even a little bit it is said to be reduced. For instance, if oxygen is removed from a carbon and is replaced by hydrogen the formal charge of carbon doesn’t change. However, the carbon has a greater share of electrons from single bond to hydrogen than it did for the single bond to oxygen. That is because hydrogen is less electronegative than oxygen and gives up its electrons more easily than the oxygen does. So a carbon bonded to hydrogen can take up more electron density than the same carbon bonded to oxygen.
Displacement reactions
Redox takes place in single displacement reactions or substitution reactions. The redox component of these types of reactions is change of oxidation state on the certain atoms, not the actual exchange of atoms in compounds.