Question

Assertion (A): Phenol is less acidic than 4-methylphenol. Reason (R): The presence of an electron releasing group in phenol makes it less acidic.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Electron-releasing groups decrease acidity of phenols; electron-withdrawing groups increase acidity.

Answer 1

The Correct Option is D

Step 1: Evaluate Assertion (A).
Assertion: Phenol is LESS acidic than 4-methylphenol. The methyl group ($-CH_3$) in 4-methylphenol is an electron-donating group. Electron-donating groups destabilise the phenoxide anion (by increasing electron density on an already negative ion), making the compound LESS acidic. So 4-methylphenol should be LESS acidic than phenol, not more acidic. The Assertion is therefore FALSE.
Step 2: Verify with $pK_a$ values.
$pK_a$ of phenol = 10.0; $pK_a$ of 4-methylphenol = 10.2. Higher $pK_a$ = weaker acid. Since 4-methylphenol has a higher $pK_a$, it is the weaker acid. Phenol is MORE acidic than 4-methylphenol. The Assertion (which claims phenol is less acidic) is FALSE.
Step 3: Evaluate Reason (R).
Reason: The presence of an electron-releasing group in phenol makes it less acidic. This is a TRUE general chemical principle. Electron-releasing groups push electron density onto the oxygen, destabilising the phenoxide anion and making the compound less willing to lose a proton (less acidic).
Step 4: Apply R to the actual situation.
In 4-methylphenol, $-CH_3$ is electron-releasing. By the Reason, this makes 4-methylphenol LESS acidic than phenol. This is the chemically correct conclusion. So R is TRUE and correctly describes a valid chemical principle.
Step 5: Match to the options.
Assertion (A) is FALSE (phenol is actually more acidic than 4-methylphenol). Reason (R) is TRUE (electron-releasing groups decrease acidity of phenols). This matches option 4.
Step 6: State the final answer.
Assertion (A) is false but Reason (R) is true. \[ \boxed{\text{Assertion (A) is false, but Reason (R) is true}} \]