27. Arrange the following in increasing order of pH.

(i) KNO3 is a salt of strong acid (HNO3) strong base (KOH), hence its aqueous solution is neutral; pH=7.
(ii) CH3COONa is a salt of weak acid (CH3COOH) and strong base (NaOH), hence, its aqueous solution is basic; pH>7.
(iii) NH4Cl is a salt of strong acid (HCl) and weak base (NH4OH) hence, its aqueous solution is acidic; pH<7.
(iv) C6H5COONH4 is a salt of weak acid, C6H5COOH and weak base, NH4OH. But NH4OH is slightly stronger than C6H5COOH. Hence, pH is slightly>7.
Therefore, increasing order of pH of the given salts is,
${\mathrm{NH}}_{4}\mathrm{Cl}<{\mathrm{C}}_{6}{\mathrm{H}}_{6}{\mathrm{COONH}}_{4}<{\mathrm{KNO}}_{3}<{\mathrm{CH}}_{3}\mathrm{COONa}$