Explain why p-nitrophenol is more acidic than phenol?


Nitro group of phenol produces - I and -R effect. Because of these two effects —NO2 group is electron withdrawing in nature. So, the electron density in the O—H bond of p-nitrophenol decreases relative to the O— H bond of phenol.

The decrease in electron density of the O—H bond of p-nitrophenol, the polarity of O—H bond is decrease and in turn make it more acidic than phenol.