How many optically active stereoisomers are possible for butane-2, 3-diol
1
2
3
4

Options

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

Explanation

To determine how many optically active stereoisomers are possible for butane-2,3-diol, we can follow these steps:

### Step 1: Identify the Structure of Butane-2,3-diol
Butane-2,3-diol has the following structure:

```
CH3
|
CH3-CHOH-CHOH-CH3
```

This compound has two chiral centers at the second and third carbon atoms.

### Step 2: Determine the Number of Stereoisomers
The formula to calculate the maximum number of stereoisomers for a compound with 'n' chiral centers is given by \(2^n\).

In the case of butane-2,3-diol:
- n = 2 (since there are 2 chiral centers)

Using the formula:
\[ \text{Number of stereoisomers} = 2^n = 2^2 = 4 \]

### Step 3: Identify the Meso Compound
Among the four stereoisomers, we need to identify if any of them are meso compounds. A meso compound has multiple stereocenters but is superimposable on its mirror image, making it optically inactive.

For butane-2,3-diol, one of the stereoisomers is a meso compound. This means we have:
- 1 meso compound (optically inactive)
- 2 other stereoisomers that are optically active (D and L forms)

### Step 4: Conclusion
Thus, the total number of optically active stereoisomers for butane-2,3-diol is:
- 2 (D and L forms)

### Final Answer
The answer is **2** optically active stereoisomers.

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