Question

What is the difference in terms of molar masses of second and fourth members of homologous series?

• A. \(12\)
• B. \(24\)
• C. \(28\)
• D. \(36\)

Hint:

Consecutive homologues differ by CH2 (14 g/mol), so the 2nd and 4th differ by two CH2 units.

Answer 1

The Correct Option is C

Step 1: Use a concrete series:
Take alkanes. The second member is ethane $\text{C}_2\text{H}_6$ (30 g/mol) and the fourth member is butane $\text{C}_4\text{H}_{10}$ (58 g/mol).

Step 2: Subtract:
$58 - 30 = 28$ g/mol.

Step 3: Generalise:
The result is the same for any homologous series, since each member adds $14$ g/mol, so the answer is C.

Final Answer:
Two members apart means two CH2 units, which is 28 g/mol. \[ \boxed{\text{(C) }28} \]