Phenols are much more acidic than alcohol due to the stabilisation of phenoxide ion resonance.
Phenoxide ion is stabilized due to following resonating structures :
While, in alcohols
Ortho nitrophenol is most acidic because in $—NO_2$ electron attracting group is attached to
ortho position which helps in stabilizing the negative charge on the oxygen of phenoxide ion. Hence, due to this reason acidic character of phenol is increased, while on attachment of $—CH_3$ group (electron donating group) acidic strength of phenol is decreased in cresol due to
the destabilization of phenoxide ion.
