- O-cresol < phenol < O- nitrophenol
Explanation:
The following order is true regarding the acidic nature of phenol.
O-cresol < phenol < O- nitrophenol.
Phenols having electron withdrawing substituents such as nitro group are more acidic due to delocalization of negative charge.
Phenols having electron releasing substituents such as alkyl group are less acidic as negative charge is not delocalised.