The acidity of benzoic acid derivatives is influenced by the para-substituent's electron-withdrawing or electron-donating properties. Electron-withdrawing groups (e.g., \( NO_2 \)) enhance acidity by stabilizing the conjugate base via delocalization. Conversely, electron-donating groups (e.g., \( OH \) or \( CH_3 \)) reduce acidity by increasing electron density on the carboxyl group. Due to its strong electron-withdrawing nature, \( p\)-NO\(_2\) stabilizes the conjugate base, thereby increasing the acidity of benzoic acid.