Isopentane on monochlorination gives....isomers and out of them ....... Are optically active.

Options

A. `3,1`
B. `4,2`
C. `3,2`
D. `4,1`

Explanation

To solve the question regarding the monochlorination of isopentane, we will follow these steps:

### Step 1: Understand the Structure of Isopentane
Isopentane, also known as 2-methylbutane, has the following structure:
```
CH3
|
CH3-CH-CH2-CH3
|
CH3
```
This structure indicates that isopentane has a branched chain.

### Step 2: Identify Possible Monochlorination Products
Monochlorination involves replacing one hydrogen atom with a chlorine atom. We can identify the positions where chlorine can be substituted:
1. Chlorination at the terminal carbon (C1).
2. Chlorination at the second carbon (C2).
3. Chlorination at the third carbon (C3).
4. Chlorination at one of the methyl groups (C4 or C5).

### Step 3: Draw the Monochlorination Products
1. **Chlorination at C1**:
- Product: 1-chloro-2-methylbutane
- Structure:
```
CH3
|
CH3-CH-CH2-CH2Cl
|
CH3
```

2. **Chlorination at C2**:
- Product: 2-chloro-2-methylbutane
- Structure:
```
CH3
|
CH3-C(Cl)-CH2-CH3
|
CH3
```
- This carbon is chiral, making this product optically active.

3. **Chlorination at C3**:
- Product: 3-chloro-2-methylbutane
- Structure:
```
CH3
|
CH3-CH-CH(Cl)-CH3
|
CH3
```
- This carbon is not chiral, making this product optically inactive.

4. **Chlorination at a Methyl Group**:
- Product: 2-chloro-3-methylbutane
- Structure:
```
CH3
|
CH2Cl-CH-CH3
|
CH3
```
- This carbon is chiral, making this product optically active.

### Step 4: Count the Isomers
From the above analysis, we have identified a total of **4 monochlorination products**:
1. 1-chloro-2-methylbutane
2. 2-chloro-2-methylbutane (optically active)
3. 3-chloro-2-methylbutane (optically inactive)
4. 2-chloro-3-methylbutane (optically active)

### Step 5: Identify Optically Active Isomers
Out of the four products, the following are optically active:
1. 2-chloro-2-methylbutane
2. 2-chloro-3-methylbutane

Thus, we have **2 optically active isomers**.

### Final Answer
Isopentane on monochlorination gives **4 isomers** and out of them **2 are optically active**.