The given diagram represents an enzyme.With reference to the lock and key model, the competitive inhibitor for the given enzyme would be

Explanation

In the lock and key model, a competitive inhibitor competes with the substrate for the active site of the enzyme. The competitive inhibitor is usually structurally similar to the normal substrate, so fits into the active site but not similar enough to catalyse the same reaction as the original substrate.The correct answer, Option B, represents a molecule structurally similar to the substrate, allowing it to bind to the active site and block substrate access. Option C and Option D are incorrect because the molecule cannot fit into the active site, as it is structurally not similar enough to bind with the enzyme's active site. Whereas Option A is exactly like the active site, making it act as a substrate rather than a competitive inhibitor.