Which one of the following substituents at para-position is most effective in stabilizing the phenoxide ion?

Electron withdrawing group stabilises the benzene ring due to delocalisation of charge. -CH3 and -CH2OH are electron-donating groups and hence decrease the stability of the benzene ring. -OCH3 is a weaker electron-withdrawing group than -COCH3. Hence, -COCH3 group more stabilizes the phenoxide ion at para-position.