The correct option is C p-Nitrophenol
carboxylic acids are more acidic than phenols and phenols are more acidic than alcohols. p-Nitrophenol is stronger acid than phenol due to -R and -I effects. p-Methoxyphenol is weaker than phenol due to (+R and -I) effects. Phenol is less acidic than acetic acid and p-Nitrophenol.