Pick the correct structure for carbolic acid among the following compounds:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → phenol, \( \ce{C6H5OH} \) (structure shown)
Carbolic acid is the old common name of phenol, hydroxybenzene, \( \ce{C6H5OH} \): an –OH group attached directly to a benzene ring. It was first isolated from coal tar, and the name records that it is weakly acidic; it reacts with sodium hydroxide to form sodium phenoxide:
\( \displaystyle \ce{C6H5OH + NaOH -> C6H5O^-Na+ + H2O} \)
The structure in Option (4), a benzene ring carrying an –OH group, is phenol.
NCERT (2026-27 edition):
Preparation of Phenols
