Which of the following is most acidic ?

Options

A. Benzyl alcohol
B. Cyclohexanol
C. Phenol
D. m-chlorophenol

Explanation

To determine which of the given compounds is the most acidic, we will analyze each option step by step.

### Step 1: Identify the Compounds
The options provided are:
1. Benzyl alcohol
2. Cyclohexanol
3. Phenol
4. Metachlorophenol

### Step 2: Classify the Compounds
- **Benzyl alcohol** and **Cyclohexanol** are both alcohols.
- **Phenol** and **Metachlorophenol** are both phenolic compounds.

### Step 3: Compare Acidity of Alcohols and Phenols
It is well-known that phenols are generally more acidic than alcohols. Therefore, we can conclude that:
- **Benzyl alcohol** and **Cyclohexanol** are less acidic than both **Phenol** and **Metachlorophenol**.

### Step 4: Focus on the Phenolic Compounds
Now we need to compare **Phenol** and **Metachlorophenol**.

### Step 5: Analyze the Effect of Substituents
- **Phenol** has a hydroxyl (-OH) group attached to a benzene ring.
- **Metachlorophenol** has a chlorine atom as a substituent at the meta position relative to the hydroxyl group.

### Step 6: Understand the Influence of Chlorine
Chlorine is an electron-withdrawing group due to its electronegativity. This means it pulls electron density away from the benzene ring.

### Step 7: Effect on the OH Bond
The presence of chlorine at the meta position causes polarization of the O-H bond in Metachlorophenol:
- The electron-withdrawing effect of chlorine increases the partial positive charge on the hydrogen atom of the hydroxyl group.
- This makes the O-H bond more polarized, which means it can break more easily.

### Step 8: Conclusion on Acidity
Since the O-H bond in Metachlorophenol is more polarized due to the presence of the electronegative chlorine atom, it can release the proton (H⁺) more readily than in Phenol. Therefore, Metachlorophenol is more acidic than Phenol.

### Final Answer
The most acidic compound among the options is **Metachlorophenol** (Option 4).

---