Final answer:
Acid phosphatase is the enzyme used as a marker for lysosomes, essential for breaking down macromolecules in an acidic environment. Therefore, the correct option is B.
Step-by-step explanation:
The enzyme used as a marker for lysosomes is acid phosphatase. Lysosomal enzymes such as acid phosphatase are crucial for the breakdown of various macromolecules. These enzymes operate at a lower pH level compared to the cytoplasm, with proton pumps maintaining the acidic environment necessary for their activity. Therefore, the correct answer to the question is (b) acid phosphatase.