Question

Which of the following set of compounds does not belong to same homologous series?

• A. CH$_4$ and C$_4$H$_{10}$
• B. C$_2$H$_6$ and C$_3$H$_8$
• C. C$_3$H$_8$ and C$_5$H$_{12}$
• D. C$_4$H$_8$ and C$_5$H$_{12}$

Hint:

Same homologous series → Same general formula. Alkanes: C$_n$H$_{2n+2}$, Alkenes: C$_n$H$_{2n}$.

Answer 1

The Correct Option is D

Concept: Compounds in the same homologous series have the same functional group and general formula and differ by a –CH$_2$ unit. Explanation:

• Alkanes follow the general formula C$_n$H$_{2n+2}$.
• C$_5$H$_{12}$ is an alkane (fits the formula).
• C$_4$H$_8$ follows C$_n$H$_{2n}$, which is the formula of alkenes.

Thus, they belong to different homologous series. Conclusion: C$_4$H$_8$ and C$_5$H$_{12}$ do not belong to the same homologous series.