When you squeeze lime juice onto sliced avocado or drip orange juice over your sliced apples, you are using citric acid as a competitive inhibitor to prevent oxygen from binding to the active site of polyphenol oxidase (PPO), the enzyme that causes fruit to turn brown. Which model best shows this inhibition?

The correct model is attached as the image.

Explanation:

In this model, there is large green circular in shape on that a medium circular indentation towards the left to the green circle. On the other hand towards the right there are two small circular indentations. There is a green smaller indention is shown as the site where oxygen binds when lime juice is squeezed on avocado.

There is two tiny gray circular structure that is joined together by a spaced line represent the oxygen that moves to bind to the active site. Arrow is connected from this gray structure to the indentation and turn back which shows inhibition. The model is given below.