o-nitrophenol , Ortho-nitrophenol is more acidic because of the presence of an electron-withdrawing group (–NO₂) at an ortho position with respect to the –OH group, which enhances the acidic strength of the compound by stabilizing the phenoxide ion and therefore, o-nitrophenol can easily release a proton.

o-cresol is less acidic due to the presence of an electron releasing group (alkyl group). They do not favour the formation of phenoxide ion. Thus, decreases the acidic strength of the compound.