Answer:
At neutral pH.
Explanation:
Trypsin and pepsin are protease enzymes that help in breakdown of large protein molecules. These enzymes are known as digestive enzymes as tripsin is produced by pancreas and pepsin is produced by stomach for digestion.
As pepsin acts on proteins in stomach, it works optimally at acidic pH. This is pH of stomach is acidic due to hydrochloric acid, produced by cells of stomach.
On the other hand, trypsin works optimally at basic pH. This is because trypsin acts on protein molecules in small intestine, where pH is slight basic due to sodium bicarbonate ions.
Thus, if pepsin and trypsin have to function together, they will show highest activity at neutral pH (pH between acidic and basic pH).