Answer: The correct answer is option(A).
Step-by-step explanation:
Optimum pH of an enzyme is defined as pH value at which activity of an enzyme is maximum or we can also say that at optimum pH reaction rate of an enzyme is highest.
Macy from her experiment observed that the starch is broken down fastest at pH 6.7. Which means that at 6.7 pH, enzyme named amylase has highest rate of breaking down the starch in a chemical reaction.
Hence, the correct answer is option (A).