Correct answer is (a) Potassium hydrogen phosphate
To explain: Potassium hydrogen phosphate and ammonium sulphate are powerful enzyme stabilizers, whereas sodium thiosulphate, calcium chloride and EDTA are enzyme destabilizers. For water molecules, the salts and proteins are competing with each other. These salts binds to charged groups which result in interaction between hydrophobic areas of enzymes. Thus making it more resistant to thermal folding. Some salts are much more effective in destabilization than stabilization which disrupts the structure of water locally.