p nitrophenol is a stronger acid than phenol while p-cresol is a weaker acid.discuss

The nitro-group is an electron-withdrawing group. The presence of this group in the para position decreases the electron density on the benzene ring. which in turn decreases the electron density on the oxygen of  O−H bond. As a result, it is easier to lose a proton. Also, the p-nitrophenoxide ion formed after the loss of protons is stabilized by resonance. Hence, ortho nitrophenol is a stronger acid.

On the other hand, methoxy group is an electron-releasing group. Thus, it increases the electron density on the oxygen of  the O−H bond and hence, the proton cannot be given out easily. For this reason, para-nitrophenol is more acidic than para-methoxyphenol.