Which one of the following does not dissolve in conc. `H_2SO_4`?

Options

A. (a) `H--=-H`
B. (b) `Me--=-Me`
C.
D. d. `H_2C=CH_2`

Explanation

To determine which compound does not dissolve in concentrated sulfuric acid (H₂SO₄), we need to analyze the stability of the carbocations formed during the electrophilic addition reaction with H₂SO₄.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- Concentrated sulfuric acid acts as a strong electrophile. When alkenes or alkynes react with it, they undergo electrophilic addition reactions, where a carbocation intermediate is formed.

2. **Analyzing the Compounds**:
- We need to evaluate the stability of the carbocation that forms when each compound reacts with concentrated sulfuric acid.

3. **Compound A**:
- For compound A (let's assume it's ethylene, C₂H₄), the reaction would form a carbocation:
\[ \text{C}_2\text{H}_4 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_2\text{H}_5^+ \]
- The carbocation (C₂H₅⁺) is highly unstable due to lack of hyperconjugation (no adjacent carbon atoms with hydrogen atoms to stabilize it). Therefore, ethylene does not dissolve in concentrated sulfuric acid.

4. **Compound B**:
- For compound B (let's assume it's propene, C₃H₆), the reaction forms a more stable carbocation:
\[ \text{C}_3\text{H}_6 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_3\text{H}_7^+ \]
- This carbocation is stabilized by hyperconjugation, making it soluble in concentrated sulfuric acid.

5. **Compound C**:
- For compound C (let's assume it's butene, C₄H₈), the carbocation formed is also stabilized by hyperconjugation:
\[ \text{C}_4\text{H}_8 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_4\text{H}_9^+ \]
- This compound is soluble in concentrated sulfuric acid.

6. **Compound D**:
- For compound D (let's assume it's isobutylene, C₄H₈), the carbocation is also stabilized:
\[ \text{C}_4\text{H}_8 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_4\text{H}_9^+ \]
- This compound is soluble in concentrated sulfuric acid as well.

7. **Conclusion**:
- Among the compounds analyzed, compound A (ethylene) does not dissolve in concentrated sulfuric acid due to the instability of the carbocation formed.

### Final Answer:
**Compound A (ethylene) does not dissolve in concentrated sulfuric acid.**