Define Homologous series and Functional group?

Surely it is much easier , quicker and you get a more detailed and valuable answer if you type into Google:
Homologous Series
and then, when you know all about homologous series, type into Google
Functional Group
You will then have the satisfaction of doing your own research , you will get a detailed answer.

A homologous series is a series of compounds where each member differs from the next member by one -CH₂- group.
For example, CH₃OH, CH₃CH₂OH, CH₃CH₂CH₂OH, CH₃CH₂CH₂CH₂OH ........

Functional groups are specific groups of atoms and bonds within molecules that are responsible for the characteristic chemical reactions of those molecules.
Common functional groups : C=C, C≡C, -Cl, -Br, -I, -OH, -O-, -CHO, C=O, -COOH, -NH₂, -NHR, -NRR', -CN, -CO2R, -COCl, -CONH₂ and -(CO)O(CO)-

functional group - a funtional group is an atom or a group of atoms that defines the structure or the chemical properties of a particular family of organic compounds

homologous series - a homologous series is a group of organic compounds having a similar structure and similar chemical propaerties in which successive compounds differ by a CH2 gropu

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