Assertion (A): 2,6-Dimethyl-4-nitrophenol (I) is more acidic than 3,5-dimethyl-4-nitrophenol (II).
Reason (R ): It is due to the steric inhibition of the resonance of `(-NO_(2))` group with two (Me) groups in (II).

Options

A. If both (A) and (R ) are true and (R ) is the correct explanation of (A).
B. If both (A) and (R ) are true but (R ) is not the correct explanation of (A).
C. If (A) is true but (R ) is false.
D. If both (A) and (R ) are false.

Explanation

To solve the question regarding the acidity of 2,6-Dimethyl-4-nitrophenol (I) and 3,5-Dimethyl-4-nitrophenol (II), we will analyze the structures and the effects of substituents on acidity step by step.

### Step 1: Understand the Structures of the Compounds
- **2,6-Dimethyl-4-nitrophenol (I)**: This compound has two methyl groups at the 2nd and 6th positions of the phenol ring and a nitro group at the 4th position.
- **3,5-Dimethyl-4-nitrophenol (II)**: This compound has two methyl groups at the 3rd and 5th positions of the phenol ring and a nitro group at the 4th position.

### Step 2: Analyze the Acidity of Phenols
- The acidity of phenols is influenced by the ability of substituents to stabilize the negative charge on the phenoxide ion (the deprotonated form of phenol).
- Electron-withdrawing groups (like -NO2) increase acidity by stabilizing the negative charge through resonance.

### Step 3: Evaluate the Effect of Substituents on Compound I
- In compound I (2,6-Dimethyl-4-nitrophenol), the nitro group can effectively stabilize the negative charge on the phenoxide ion through resonance without significant steric hindrance from the methyl groups.

### Step 4: Evaluate the Effect of Substituents on Compound II
- In compound II (3,5-Dimethyl-4-nitrophenol), the presence of two methyl groups at the 3rd and 5th positions creates steric hindrance. This steric hindrance inhibits the resonance effect of the nitro group, making it less effective in stabilizing the negative charge on the phenoxide ion.

### Step 5: Compare the Acidity
- Due to the steric hindrance in compound II, the nitro group is less effective in stabilizing the negative charge compared to compound I. Therefore, compound I is more acidic than compound II.

### Conclusion
- **Assertion (A)**: 2,6-Dimethyl-4-nitrophenol (I) is more acidic than 3,5-Dimethyl-4-nitrophenol (II) - This is true.
- **Reason (R)**: The reason provided is that it is due to the steric inhibition of the resonance of the nitro group with the two methyl groups in compound II - This is also true and correctly explains the assertion.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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