Question

Observe the following pairs of organic compounds:

(I) $C_4{H}_{9}OH$ and $C_5{H}_{11}OH$
(II) $C_5{H}_{11}OH$ and $C_7{H}_{15}OH$
(III) $C_3{H}_{7}OH$ and $C_6{H}_{13}OH$

Which of these pairs belong to the same homologous series?

• A. (III) only
• B. (II) only
• C. (I) only
• D. All of these

Answer 1

The correct option is D All of these

Homologous series is a series of compounds with similar chemical properties and the same functional group, differing from the successive member by $-C{H}_2$.
When we observe in $\left(I\right)$, molecules differ by $-C{H}_2$
When we observe in $\left(II\right)$, molecules differ by $-C_2{H}_4$
When we observe in $\left(III\right)$, molecules differ by $-C_3{H}_6$
All these molecules differ by a multiple of $-C{H}_2$ and have the same functional group, hence all these molecules belong to the same homologous series.