Question

The molecular formula of compound A and B are $C_3{H}_6{O}_2$ and $C_3{H}_{8}O$ respectively. A and B respectively belong to homologous series of:

• A. Carboxylic acids and Ketones
• B. Carboxylic acids and Alcohols
• C. Alcohols and Ketones
• D. Alcohols and Aldehydes

Answer 1

The correct option is B Carboxylic acids and Alcohols

Homologous series is a series of compounds with same functional group. Since oxygen is present as heteroatom in the compounds A and B, the functional groups present can be alcohols, aldehydes, ketones or carboxylic acid. The general formula for homologous series of alcohols, aldehydes, ketones and carboxylic acid is given in the table below.

$\begin{array}{ccc}\text{Class of compounds}& \text{General formula}& n\\ \text{Alcohol}& C_n{H}_{2n+2}O& n=1,2,\mathrm{3...}\\ \text{Aldehyde}& C_n{H}_{2n}O& n=1,2,\mathrm{3...}\\ \text{Ketone}& C_n{H}_{2n}O& n=3,4,\mathrm{5...}\\ \text{Carboxylic acid}& C_n{H}_{2n}{O}_2& n=1,2,\mathrm{3....}\end{array}$

In compound A and B, three carbon atoms are present. By putting n =3, we obtain molecular formula for alcohol to be $C_3{H}_{8}O$ and carboxylic acid to be $C_3{H}_6{O}_2$. Therefore compound A ($C_3{H}_6{O}_2$) and compound B ($C_3{H}_{8}O$) belongs to the homologous series of carboxylic acid and alcohol respectively.