Which of the following reagents cannot be used to distinguish between phenol and benzyl alcohol ?

Options

A. `Br_2//"CCl"_4`
B. NaOH
C. `NaHCO_3`
D. `FeCl_3` (neutral)

Answer

To determine which reagent cannot be used to distinguish between phenol and benzyl alcohol, we will analyze the reactions of each reagent with both compounds.

### Step-by-Step Solution:

1. **Identify the Structures:**
- Phenol: C6H5OH (hydroxyl group attached to a benzene ring)
- Benzyl Alcohol: C6H5CH2OH (hydroxyl group attached to a benzyl group)

2. **Analyze the Reagents:**
- **Br2/CCl4 (Bromine in Carbon Tetrachloride):**
- When phenol reacts with Br2/CCl4, it forms tribromophenol (a brominated product).
- Benzyl alcohol does not react with Br2/CCl4 in the same way.
- Therefore, this reagent can distinguish between phenol and benzyl alcohol.

3. **Sodium Hydroxide (NaOH):**
- When phenol reacts with NaOH, it forms sodium phenoxide (phenolate ion) and water.
- Benzyl alcohol does not react with NaOH.
- Thus, NaOH can also distinguish between the two.

4. **Sodium Bicarbonate (NaHCO3):**
- Both phenol and benzyl alcohol do not react with NaHCO3.
- Since neither compound shows a reaction, this reagent cannot be used to distinguish between them.

5. **Neutral Iron(III) Chloride (FeCl3):**
- Phenol gives a color change (purple complex) when reacted with FeCl3.
- Benzyl alcohol does not show any color change.
- Therefore, FeCl3 can also distinguish between the two.

6. **Conclusion:**
- The reagent that cannot be used to distinguish between phenol and benzyl alcohol is **Sodium Bicarbonate (NaHCO3)**.

### Final Answer:
The correct answer is **NaHCO3**.