A : Ortho - cresol is weaker acidic than meta-cresol .
R : It is due to ortho effect .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

To solve the assertion-reason question regarding ortho-cresol and meta-cresol, we will analyze both the assertion and the reason step by step.

### Step 1: Understanding the Assertion
The assertion states that "Ortho-cresol is weaker acidic than meta-cresol." To evaluate this, we need to understand the acidity of these compounds.

- **Ortho-cresol (2-cresol)** has the hydroxyl (-OH) group and a methyl (-CH3) group adjacent to each other on the benzene ring.
- **Meta-cresol (3-cresol)** has the hydroxyl group and the methyl group separated by one carbon atom.

### Step 2: Analyzing the Acidity
The acidity of phenolic compounds is influenced by the stability of the phenoxide ion formed after deprotonation (removal of the hydrogen from the -OH group).

- When ortho-cresol loses a proton, it forms the ortho-phenoxide ion. The presence of the adjacent methyl group (due to the +I effect) increases electron density on the ring, which destabilizes the negative charge on the ortho-phenoxide ion.
- In contrast, when meta-cresol loses a proton, it forms the meta-phenoxide ion. The methyl group is further away, and thus its +I effect has a lesser impact on the stability of the negative charge on the meta-phenoxide ion.

### Step 3: Conclusion on Acidity
Since the ortho-phenoxide ion is less stable due to the destabilizing effect of the adjacent methyl group, ortho-cresol is indeed a weaker acid compared to meta-cresol, which has a more stable phenoxide ion.

### Step 4: Understanding the Reason
The reason states, "It is due to ortho effect." The ortho effect typically refers to the increased acidity of ortho-substituted carboxylic acids compared to their meta counterparts due to intramolecular hydrogen bonding or steric effects. However, this effect does not apply to phenols in the same way.

### Final Conclusion
- The assertion is **true**: ortho-cresol is weaker acidic than meta-cresol.
- The reason is **false**: the ortho effect does not explain the acidity difference in phenols.

Thus, the correct answer is that the assertion is true, but the reason is false.