The pH of 0.1 M solution of the following species increases in the order

(i) HCl is a strong acid. Hence its pH is lowest among the others. (ii) NaCl is a salt of strong acid and strong base so it is not hydrolyzed and hence its pH is 7.(iii) NH4Cl+H2O⇌NH4OH+HCl∴ The solution is acidic and pH is less than that of 0.1 M HCl. (iv) NaCN + H2O ⇌ NaOH + HCN∴ The solution is basic and pH is more than that of 0.1 M HCl. ∴Correct order for increase in pH isHCl < NH4Cl < NaCl < NaCN.