In phenols, the presence of electron releasing groups decrease the acidity, whereas presence of electron withdrawing groups increase the acidity, compared to phenol. Among the meta and para-nitrophenols, the latter is more acidic as the presence of −NO2 group at para position stabilises the phenoxide ion to a greater extent than when it is present at meta position. Thus, correct order of acidity is : Para-nitrophenol > meta-nitrophenol > phenol > methyl phenol (iv) (iii) (i) (ii)