On which part of the enzyme is the enzyme-substrate complex formed?

Explanation

The correct answer is Option B: Binding site. The enzyme-substrate complex is formed at the binding site, which is a specific region within the active site of the enzyme. The active site facilitates the binding of the substrate and the subsequent chemical reaction, but the term 'binding site' more accurately describes the specific location where the substrate interaction occurs. Option A is incorrect because it unnecessarily combines two terms, Option C is incorrect as it is less specific, and Option D is incorrect because an apoenzyme is not involved in substrate binding.