The reagents involved in the following conversion are

$NaOH,CO_2, H^+$

The correct answer is Option (2) → $NaOH,CO_2, H^+$

The conversion of phenol to salicylic acid (o-hydroxybenzoic acid) is carried out by treating phenol with NaOH and CO₂ followed by acidification (H⁺). This reaction is known as the Kolbe–Schmitt reaction.

First, phenol reacts with NaOH to form sodium phenoxide. This then reacts with CO₂ under pressure to introduce a –COOH group at the ortho position. Finally, acidification (H⁺) converts the salt into salicylic acid.