(N/A) The increasing order of acidic strength is: $o-\text{cresol} < \text{phenol} < o-\text{nitrophenol}$.
Explanation:
$1$. The acidity of phenols depends on the stability of the phenoxide ion formed after the loss of a proton $(H^+)$.
$2$. The $-CH_3$ group in $o-\text{cresol}$ is an electron-donating group ($+I$ and hyperconjugation effect),which destabilizes the phenoxide ion,thereby decreasing the acidic strength compared to phenol.
$3$. The $-NO_2$ group in $o-\text{nitrophenol}$ is a strong electron-withdrawing group ($-I$ and $-M$ effects),which stabilizes the phenoxide ion by dispersing the negative charge,thereby significantly increasing the acidic strength compared to phenol.