The correct acidity order of the following is
(I) (see structure)
(II) (see structure)
(III) (see structure)
(IV) (see structure)
I 
II 
III 
IV
(I) (see structure)
(II) (see structure)
(III) (see structure)
(IV) (see structure)
- (A)(III) > (IV) > (II) > (I)✓ Correct
- (B)(IV) > (III) > (I) > (II)
- (C)(III) > (II) > (I) > (IV)
- (D)(II) > (III) > (IV) > (I)
Answer: (A)
Solution
The acidity of these compounds depends on the stability of their conjugate bases:
The order of acidity is:
III > IV > II > I
Therefore, the answer is (A).
- (I) Phenol: weakly acidic (pKa ≈ 10)
- (II) p-Chlorophenol: Cl is electron-withdrawing, increases acidity (pKa ≈ 9.4)
- (III) Benzoic acid: carboxylic acid, most acidic (pKa ≈ 4.17)
- (IV) p-Methylbenzoic acid: CH₃ is electron-donating, slightly less acidic than benzoic acid (pKa ≈ 4.37)
The order of acidity is:
III > IV > II > I
Therefore, the answer is (A).
JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · Single correct option