Read the passage carefully and answer the questions.

Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively is replaced by - OH group. These are further classified on the basis of number of hydroxy groups and according to the hybridization of the carbon atom $sp^2$ or $sp^3$ to which the -OH group is attached. They find applications in industry as well as in day-to-day life. One of the most commercially obtained alcohol also known as wood spirit is obtained by destructive distillation of wood. Both alcohols and phenols are acidic in nature. The acidity of alcohols and phenols vary according to the nature of substituent(s) attached to them. Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters. Introduction of acetyl group in alcohols and phenols is called acetylation. Phenol undergo electrophilic aromatic substitution reaction because the -OH activates the benzene ring. It undergoes nitration, halogenation and sulphonation reactions.

Identiify the strongest acidic compound

p-Nitrophenol

The correct answer is Option (2) → p-Nitrophenol 

The acidity of phenols depends on the stability of the phenoxide ion formed after losing a proton.

Substituents on the benzene ring affect acidity through:

• Electron-withdrawing groups (–I, –M effects) → Increase acidity by stabilizing phenoxide ion

• Electron-donating groups (+I, +M effects) → Decrease acidity by destabilizing phenoxide ion

Effect of substituents in the given compounds

Phenol Phenol itself has moderate acidity due to resonance stabilization of the phenoxide ion.

p-Nitrophenol The –NO₂ group is a strong electron-withdrawing group showing both –I and –M effects. This strongly stabilizes the phenoxide ion, making the release of H⁺ easier and increasing acidity.

Thus p-nitrophenol is much more acidic than phenol.

p-Cresol The –CH₃ group is an electron-donating group (+I effect). It increases electron density on the ring and destabilizes the phenoxide ion, thereby decreasing acidity.

p-Methoxyphenol The –OCH₃ group shows a strong +M (electron-donating) effect, increasing electron density on the ring and reducing acidity.