KCET 2015 Chemistry Solved Paper

Nitro group has both –R effect and –I effect; but –R effect predominates. Due to stronger electron withdrawing nature of NO2 group, phenoxide ion is stabilized. Hence, m-nitrophenol is more acidic than phenol. Methyl group destabilizes the phenoxide ion by +I effect and hyperconjugation. Hence m-cresol is weaker acid than phenol. Chlorine have both +R and –I effect but –I effect predominates
Hence m-chlorophenol is more acidic than phenol. –R effect of nitro group is stronger than –I effect of chlorine hence, m-nitrophenol is more acidic than m-chlorophenol.
Therefore, the correct order of acidic strength is m-nitrophenol > m-chlorophenol > phenol > m-cresol.