Correct option is (a) Activity profile of immobilized enzymes against pH
For explanation I would say: The pH of micro and bulk environment depends on whether H^+ ions are being attracted or repelled by the charge on immobilized enzyme. Now, as the binding substrate and activity of immobilized enzyme depends on the local micro-environmental pH, this portioning cause an appropriate shift in Km with respect to other solution. This is a commonly used method to alter the pH. The diagram represents the profile of activity of an enzyme, immobilized on charged supports with pH of the solution. In this diagram, ‘a’ represents free enzyme, ‘b’ represents enzyme bound to anionic support and ‘c’ represents enzyme bound to cationic support. In case ‘b’, a bulk of pH 5 is needed to produce a product of pH 7 in microenvironment. In case ‘c’, a bulk pH of 9 is needed to produce a pH of 7 in microenvironment.