Question

Successive compounds in the homologous series differ by a _____ group.

• A. \( CH_3 \)
• B. \( CH_4 \)
• C. \( CH_2 \)
• D. \( C_2H_2 \)

Hint:

In a homologous series:
• Functional group remains same.
• Consecutive members differ by \( CH_2 \).
• Molecular mass increases by \(14\).

Answer 1

The Correct Option is C

Concept:
A homologous series is a family of organic compounds having:
• Same functional group
• Similar chemical properties
• Gradual change in physical properties Successive members differ by one: \[ \boxed{CH_2} \] unit. Examples of alkane homologous series: \[ CH_4,\ C_2H_6,\ C_3H_8,\ C_4H_{10} \] Observe: \[ C_2H_6 - CH_4 = CH_2 \] \[ C_3H_8 - C_2H_6 = CH_2 \]

Step 1: Understand homologous series.
In organic chemistry, compounds arranged in a sequence where each next member differs by: \[ CH_2 \] are called homologous series.

Step 2: Check all given options carefully.
Option (A): \( CH_3 \)
Incorrect because homologous compounds do not differ by \(CH_3\). Option (B): \( CH_4 \)
Incorrect because methane itself is a compound, not the common difference. Option (C): \( CH_2 \)
Correct because every successive member increases by one methylene group. Hence, correct. Option (D): \( C_2H_2 \)
Incorrect because homologous members do not differ by this unit.

Step 3: Select the correct answer.
Therefore, successive compounds differ by: \[ \boxed{CH_2} \] Hence, \[ \boxed{(3)\ CH_2} \]