Homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group.
Example of Homologous series: All the alkanes have similar structures with single covalent bonds and show similar chemical properties, so they can be grouped together in the form of a homologous series.
Homologous series of alkanes: Methane- CH4, Ethane- C2H6, Propane- C3H8, Butane- C4H10, Pentane- C5H12.