p-Nitrophenol is a stronger acid than phenol while p-cresol is a weaker acid . This can be explained as

Explanation

The `-NO_(2)` group is an electron withdrawing group. When present at the para position in the ring, it decreases the electron density on the oxygen atom of `O-H` group due to conjugation and the release of `H^(+)` ion becomes easier than in phenol. On the other hand, `-CH_(3)` group is an electron releasing group. It increases the electron density on the oxygen atom and the release of `H^(+)` ion becomes difficult compared to phenol. therefore, p-nitrophenol is a stronger acid than phenol while p-cresol is a weaker acid. For further details, consult section 16 (Chemical properties of phenols).