Final answer:
To inhibit browning of apples, use condition d) Low temperature and acidic pH, since deviating from the enzyme catechol oxidase's optimal conditions by lowering temperature and pH will reduce its activity.
Step-by-step explanation:
To prevent the browning of apple slices for a party, given that the enzyme catechol oxidase works best at a temperature of 25 degrees Celsius and a pH of 7, the condition you would use is d) Low temperature and acidic pH. This is because high temperatures can cause enzymes to denature, which leads to a loss of their three-dimensional structure and function. Furthermore, since enzymes have an optimal pH range for activity, moving away from this range, particularly towards extreme pH values, can also lead to denaturation. A lower temperature will slow down the reaction rate, and an acidic pH will hinder the enzyme's activity, thus preventing the oxidative browning that occurs when apples are exposed to air.