Which of the following reactions would give `pentan-2-ol` ?

Options

A.
B.
C.
D. `MeCHO overset(PrmgBr//ether) underset (H_3 O^(oplus))rarr`

Explanation

To determine which of the given reactions would yield pentan-2-ol, we need to analyze each option step by step. Pentan-2-ol has the following structure:

```
CH3
|
CH3-CH-CH2-CH3
|
OH
```

This indicates that the hydroxyl group (-OH) is attached to the second carbon of a five-carbon chain (pentane).

### Step 1: Analyze Each Option

**Option 1:**
- The reaction involves a Grignard reagent (R-MgBr) reacting with a carbonyl compound (ketone or aldehyde).
- If we assume the carbonyl compound is a ketone like butan-2-one (CH3-CO-CH2-CH3), the Grignard reagent (e.g., CH3MgBr) adds to the carbonyl carbon, forming a tertiary alcohol after hydrolysis.
- The final product will be pentan-2-ol.

**Option 2:**
- Similar to Option 1, if we use a Grignard reagent with a different carbonyl compound, such as propan-2-one (CH3-CO-CH3), and add CH3MgBr, we can also form pentan-2-ol after hydrolysis.
- The reaction will yield pentan-2-ol as well.

**Option 3:**
- In this case, if we start with a compound like 1-bromopropane (CH3-CH2-CH2-Br) and react it with a Grignard reagent (e.g., CH3MgBr), the product after hydrolysis will also yield pentan-2-ol.
- The mechanism involves the formation of a new carbon-carbon bond, leading to the desired alcohol.

**Option 4:**
- Here, if we start with a carbonyl compound like butanal (CH3-CH2-CHO) and react it with a Grignard reagent, we can also achieve pentan-2-ol.
- The addition of the Grignard reagent to the carbonyl, followed by hydrolysis, will yield pentan-2-ol.

### Conclusion

All four options can lead to the formation of pentan-2-ol through different pathways involving Grignard reagents and appropriate carbonyl compounds.

### Final Answer
All options (1, 2, 3, and 4) would give pentan-2-ol.

---