Which of the following are more acidic than phenol?

Electron-withdrawing groups (nitro; chloro by its $-I$ effect) stabilise the phenoxide ion and raise acidity ($\mathrm{p}{K}_a$ 7.15 and 9.1 against 9.95). Electron-releasing groups such as methyl and amino destabilise the phenoxide, so those phenols are weaker acids ($\mathrm{p}{K}_a\approx 10.3$).