The correct answer is (c) KW/KaKb
Easiest explanation: The hydrolysis constant of a weak acid and weak base is KW/KaKb, the degree of hydrolysis is √KW/KaKb and the pH of the solution is given by 1/2pKW + 1/2pKa – 1/2pKb. An example of a salt of a weak acid and a weak base is CH3COOHNH4.