Pepsin activity in acidic conditions Steps:

• Pepsin is a protease enzyme that digests proteins but requires low pH for activation.
• Hydrochloric acid lowers pH, enabling pepsin to break down agar proteins effectively.
• Boiled pepsin denatures, losing enzymatic function.
• Distilled water lacks enzyme or acid, preventing digestion. Why B is correct:
• Pepsin with HCl provides optimal acidic pH (around 2) for maximum proteolytic activity, clearing the largest protein-free zone. Why the others are wrong:
• A: Pepsin alone functions poorly at neutral pH of agar, limiting digestion.
• C: Boiling denatures pepsin, eliminating its ability to hydrolyze proteins.
• D: Water has no digestive agents, so no protein breakdown occurs.

Final answer: B