Which of the following is most acidic?
(i) Benzyl alcohol
(ii) Cyclohexanol
(iii) Phenol
(iv) m-Chlorophenol
The answer is the option (iv). The addition of electron-withdrawing groups in phenol increases its acidity, whereas the addition of electron-donating groups decreases the acidity. And as a known fact, that the (+R) effect duet to donating is dominant over the (+I) effect. But this is only feasible in the case of substituents at ortho and para positions.
Keeping the above-mentioned point in mind, the m-Chlorophenol compound is the most acidic of all four options. So, option (iv) is the answer.