In Kolbe's reaction, phenol undergoes:

Electrophilic substitution

The correct answer is option 2. Electrophilic substitution.

Phenol reacts with sodium hydroxide and carbon dioxide under specific conditions to produce salicylic acid. This reaction is known as the Kolbe-Schmitt reaction.

Phenol \((C_6H_5OH)\) first reacts with sodium hydroxide \((NaOH)\) to form sodium phenoxide \((C_6H_5O^-Na^+)\). The sodium phenoxide then reacts with carbon dioxide \((CO_2)\) under high pressure and temperature to form sodium salicylate.The sodium salicylate is then treated with an acid (like hydrochloric acid, \(HCl\)) to form salicylic acid.

Salicylic Acid: The final product is salicylic acid, which has the formula \(C_6H_4(OH)(COOH)\). It is an ortho-hydroxybenzoic acid.

Mechanism: Kolbe's reaction is characterized by the decarboxylation of phenol (or its salts), not by electrophilic substitution. The primary result of Kolbe's reaction is the formation of benzene from phenol.