Question

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

• A. \(\text{CH}_4\)
• B. \(\text{C}_2\text{H}_6\)
• C. \(\text{C}_3\text{H}_4\)
• D. \(\text{C}_4\text{H}_{10}\)

Hint:

Always check compounds against the \(C_n H_{2n+2}\), \(C_n H_{2n}\), and \(C_n H_{2n-2}\) formulas to quickly identify their homologous series.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A homologous series is a family of organic compounds that share the same general formula and similar chemical properties.

Step 2: Detailed Explanation:
Let's test the given formulas against general formulas for hydrocarbons:
Alkanes: \(C_n H_{2n+2}\)
Alkenes: \(C_n H_{2n}\)
Alkynes: \(C_n H_{2n-2}\)
Option (A) \(\text{CH}_4\): \(n=1\), \(H = 2(1)+2 = 4\). This is an alkane (Methane).
Option (B) \(\text{C}_2\text{H}_6\): \(n=2\), \(H = 2(2)+2 = 6\). This is an alkane (Ethane).
Option (D) \(\text{C}_4\text{H}_{10}\): \(n=4\), \(H = 2(4)+2 = 10\). This is an alkane (Butane).
Option (C) \(\text{C}_3\text{H}_4\): \(n=3\), \(H = 2(3)-2 = 4\). This fits the alkyne formula (\(C_n H_{2n-2}\)). It is Propyne.
Since options A, B, and D are alkanes, option C (an alkyne) is the odd one out and does not belong to the same homologous series.

Step 3: Final Answer:
\(\text{C}_3\text{H}_4\) is not an alkane.