Reduction
Reduction is referred to as addition of hydrogen to an
unsaturated group like a carbon-carbon double bond, a carbonyl group or an
aromatic nucleus.
Addition of hydrogen with fission of a bond between two atoms
is also referred to as reduction.
For example,
1)
Conversion of ethylene into ethane
2)
Conversion of acetaldehyde into ethyl alcohol
In reduction the
oxidation number changes from higher oxidation states to a lower oxidation
state.