Arrange the following in increasing order of their $pK_a$, values.
(A) o-nitrophenol
(B) m-nitrophenol
(C) Phenol
(D) Ethanol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C), (D)
pKₐ increases as acidity decreases.
Relative acidity of the given compounds:
- o-Nitrophenol → strongest acid (−I and −R effects of NO₂)
- m-Nitrophenol → slightly less acidic (−I effect only)
- Phenol → weaker acid
- Ethanol → weakest acid
So, increasing order of pKₐ values is:
$\text{o-Nitrophenol (A)} < \text{m-Nitrophenol (B)} < \text{Phenol (C)} < \text{Ethanol (D)}$