Question

Given below are two statements:
One is labelled as Assertion A and the other is labelled as Reason R: 
Assertion A: \(pK_a\)​ value of phenol is 10.0 while that of ethanol is 15.9. 
Reason R: Ethanol is stronger acid than phenol. 
In the light of the above statements, choose the correct answer from the options given below:

• A. A is true but R is false.
• B. A is false but R is true.
• C. Both A and R are true and R is the correct explanation of A.
• D. Both A and R are true but R is NOT the correct explanation of A.

Answer 1

The Correct Option is A

The problem involves understanding the acidity of phenol and ethanol, characterized by their \( pK_a \) values. 

1. Understanding \( pK_a \) Value:
   • \( pK_a \) is the negative logarithm of the acid dissociation constant (\( K_a \)), an indicator of the strength of an acid.
   • The lower the \( pK_a \) value, the stronger the acid, as it indicates a greater tendency to lose a proton (H⁺).
2. Given Data:
   • \( pK_a \) of phenol = 10.0
   • \( pK_a \) of ethanol = 15.9
3. Assertion (A):
   • The assertion states that the \( pK_a \) value of phenol is 10.0, while that of ethanol is 15.9. This is true.
4. Reason (R):
   • The reason claims that ethanol is a stronger acid than phenol. This is false because, as explained, lower \( pK_a \) means a stronger acid, and phenol has a lower \( pK_a \) than ethanol.
5. Conclusion:
   • Considering the values and their implications, the correct option is: A is true but R is false.

Answer 2

Phenol is more acidic than ethanol because the conjugate base of phenoxide is more stable than ethoxide due to resonance stabilization in phenoxide.
Thus, the correct answer is Option A.