Which graph shows the effect of $\mathrm{pH}$ on enzyme activity?

. The curve in option (c) correctly represents the effect of pH on enzyme activity. Enzyme shows its highest activity at a particular pH called the optimum pH. Activity declines both below and above the optimum value.
This can be easily represented using the graph given in option (c). Changes in pH also alter the shape of an enzyme’s active site. Each enzyme work bests at a specific pH value. The optimum pH for an enzyme depends on where it normally works. As the pH increases so does the rate of enzyme activity. A continued increase in pH results in a sharp decrease in activity as the enzyme’s active site changes shape. It is now denatured.
Therefore, option (c) is correct.