When `H_(2)` is added to two isomeric alkenes A and B having molecular formula `C_(5)H_(9)Cl`, A gives optically inactive compound while B gives a chiral compound. The two isomers are

Options

A. 3 - chloro -2- pentene and 2 - chloro -2- pentene
B. 4 - chloro -1- pentene and 2 - chloro -2- pentene
C. 3 - chloro -1- pentene and 4 - chloro -2- pentene
D. 1 - chloro -1- pentene and 5 - chloro -1- pentene

Answer

To solve the problem, we need to identify two isomeric alkenes with the molecular formula C5H9Cl. One of these isomers (A) should yield an optically inactive compound upon hydrogenation, while the other isomer (B) should yield a chiral compound.

### Step 1: Identify the possible isomers of C5H9Cl
The molecular formula C5H9Cl indicates that we have a five-carbon chain with one chlorine atom and a degree of unsaturation (due to the presence of a double bond). The possible structural isomers can include different positions of the double bond and the chlorine atom.

### Step 2: Consider the structure of isomer A
Let's consider the structure of **3-chloro-2-pentene** (isomer A):
- The structure can be represented as follows:
```
CH3-CH=CH-CH2-CH2Cl
```
- Upon hydrogenation (adding H2), the double bond will be saturated, resulting in **3-chloro-2-pentane**:
```
CH3-CH(CH2Cl)-CH2-CH3
```
- This compound has two equivalent ethyl groups (C2H5) attached to the same carbon, making it **optically inactive**.

### Step 3: Consider the structure of isomer B
Now, let's consider the structure of **2-chloro-2-pentene** (isomer B):
- The structure can be represented as follows:
```
CH3-CH2-C(Cl)=CH-CH3
```
- Upon hydrogenation, this will yield **2-chloro-2-pentane**:
```
CH3-CH2-C(Cl)-CH2-CH3
```
- Here, the carbon with the chlorine atom is attached to four different groups (methyl, ethyl, propyl, and hydrogen), making it **chiral** and thus **optically active**.

### Conclusion
The two isomers are:
- Isomer A: **3-chloro-2-pentene** (gives optically inactive compound)
- Isomer B: **2-chloro-2-pentene** (gives chiral compound)

### Final Answer
The two isomers are **3-chloro-2-pentene** (A) and **2-chloro-2-pentene** (B).