What is meant by aan echo ? Explain.

Explanation

(i) You have seen that chains of different length are formed by joining the carbon atoms to each other. Moreover you have also seen that a functional group can take place of hydrogen atom on these chains.
(ii) As a result, large number of compounds are formed having same functional group but different length of carbon chain. For example, there are many compounds such as `CH_(3)-OH, CH_(3)-CH_(2)-OH, CH_3-CH_2-CH_2-OH, CH_3-CH_2-CH_2-CH_2OH` which contain alcohol as the functional group.
(iii) Though the length of the carbon chain in them is different, their chemical properties are very much similar due to the presence of the same functional group in them.
(iv) The series of compounds formed by joining the same functional group in the place of a particular a hydrogen atom on the chains having sequentially increasing length is called homologous series.
(v) There are different homologous series accordance with the functional group. For example, homologous series homologous homologous series of aldehydes, etc.
(vi) All the members of the homologous series are homologues of each other. Homologous series of alkanes is: `CH_(4)"Methane" " "C_(2)H_(6)"Ethane"`
C_(3)H_(8)"Propane"" "C_(4)H_(10)"Butane"`