Concept:A trihydric phenol contains three hydroxyl (
−OH) groups attached directly to the benzene ring.
Explanation:Catechol is 1,2-dihydroxybenzene, having two
−OH groups, so it is dihydric.
Resorcinol is 1,3-dihydroxybenzene, also dihydric.
Quinol (hydroquinone) is 1,4-dihydroxybenzene, also dihydric.
Pyrogallol is 1,2,3-trihydroxybenzene, containing three
−OH groups.
Therefore, pyrogallol is the trihydric phenol among the given options.
Answer:B. Pyrogallol
