According to the graph, the enzymes have different optimum pH as the curves do not overlap.
The answer of question a is: False
In terms of bonding, the rate of the reaction falls gradually once the pH increases above the optimum rather than denaturing, because the enzyme might suffer certain modifications that may decrease its affinity towards the sustrate, or alter its active site, but not necessary degrade, or denature the whole molecule. This proccess doesn't occur at a minimal pH change.
