▪In organic chemistry, a homologous series is a series of compounds with the same functional group and similar chemical properties in which each successive member differs by CH2. ... Compounds within a homologous series typically have a fixed set of functional groups that gives them similar chemical and physical properties.

●Just take alkane of alkali group with chemical formula CnH2n+2......where n is the number of molucle we put in the compound.
●Now when we put 1 molucle in the formulae then it become CH4(Methane), and just after that we put 2 molcule in the above formulae it become C2H6(Ethane).
●Now the difference od both of compound will be CH2.
● In the same way if u take any regular compound of the same group then their molucular difference will always constant and equalas to CH2. This is called homologous series.

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A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group...... For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2.