An optically active hydrocarbon `X` has molecular formula `C_(6)H_(12)`. `X` on catalytic hydrogenation gives optically inactive `C_(6)H_(14).X` could be

Options

A. `3-` methyl`-1-`pentene
B. `3-`methl`-2-`pentene
C. `4-`methl`-2-`pentene
D. `2-`ethyl `-1-`butene

Explanation

To solve the problem, we need to identify the optically active hydrocarbon \( X \) with the molecular formula \( C_6H_{12} \) that, upon catalytic hydrogenation, produces an optically inactive compound \( C_6H_{14} \).

### Step-by-Step Solution:

1. **Understanding Optically Active Compounds**:
- An optically active compound contains at least one chiral carbon atom. A chiral carbon atom is a carbon atom that is attached to four different groups, leading to non-superimposable mirror images (enantiomers).

2. **Molecular Formula Analysis**:
- The molecular formula \( C_6H_{12} \) indicates that the compound is likely an alkene (due to the degree of unsaturation).

3. **Identifying Possible Structures**:
- We need to consider the possible structures of \( C_6H_{12} \) that could be optically active. The presence of a double bond and the arrangement of substituents can create chirality.

4. **Evaluating the Given Options**:
- **Option 1: 3-methyl-1-pentene**:
- Structure: \( CH_3-CH_2-CH=CH-CH_3 \) with a methyl group on the third carbon.
- This compound has a chiral center at the third carbon, making it optically active.

- **Option 2: 3-methyl-2-pentene**:
- Structure: \( CH_3-CH=CH-CH_2-CH_3 \).
- This compound does not have a chiral center; thus, it is not optically active.

- **Option 3: 4-methyl-2-pentene**:
- Structure: \( CH_3-CH=CH-CH(CH_3)-CH_3 \).
- This compound also does not have a chiral center and is not optically active.

- **Option 4: 2-ethyl-1-butene**:
- Structure: \( CH_2=CH-CH_2-CH_3 \) with an ethyl group on the second carbon.
- This compound does not have a chiral center and is not optically active.

5. **Catalytic Hydrogenation**:
- When we perform catalytic hydrogenation on 3-methyl-1-pentene, the double bond is converted to a single bond, resulting in 3-methylpentane.
- Structure of 3-methylpentane: \( CH_3-CH_2-CH(CH_3)-CH_2-CH_3 \).
- This compound does not have any chiral centers, making it optically inactive.

6. **Conclusion**:
- The only compound that meets the criteria of being optically active and yielding an optically inactive product upon hydrogenation is **3-methyl-1-pentene**.

### Final Answer:
**X could be 3-methyl-1-pentene.**