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

Options

A. `C_2H_4`
B. `C_2H_2`
C. `C_4H_8`
D. `C_3H_6`

Explanation

To determine which of the given hydrocarbons does not belong to the same homologous series, we need to analyze the compounds based on their chemical formulas and identify their types.

### Step-by-Step Solution:

1. **Identify the Compounds**: The given compounds are C2H4, C2H2, C4H8, and C3H6.

2. **Determine the Type of Each Compound**:
- **C2H4**: This compound has 2 carbon atoms and 4 hydrogen atoms. It follows the general formula for alkenes, which is CnH2n. Here, n = 2, so it is an alkene.
- **C2H2**: This compound has 2 carbon atoms and 2 hydrogen atoms. It follows the general formula for alkynes, which is CnH2n-2. Here, n = 2, so it is an alkyne.
- **C4H8**: This compound has 4 carbon atoms and 8 hydrogen atoms. It follows the general formula for alkenes, which is CnH2n. Here, n = 4, so it is also an alkene.
- **C3H6**: This compound has 3 carbon atoms and 6 hydrogen atoms. It follows the general formula for alkenes, which is CnH2n. Here, n = 3, so it is also an alkene.

3. **Compare the Compounds**:
- C2H4, C4H8, and C3H6 are all alkenes (CnH2n).
- C2H2 is an alkyne (CnH2n-2).

4. **Conclusion**: Since C2H2 is the only compound that is an alkyne while the others are alkenes, it does not belong to the same homologous series as the others.

### Final Answer:
The compound that does not belong to the same homologous series is **C2H2** (option B).