The question asks to identify compound $A$ in a chemical reaction, but the actual reaction scheme/image is missing from the prompt. Also, the options A, B, C, D are blank.

So, there is not enough chemical information to determine the product/reactant.

Step-by-step assessment

1. To identify $A$, we need the reaction details such as:

   • starting compound,
   • reagents/conditions,
   • products/intermediates,
   • and the given answer choices.

2. In the present prompt, only the statement is available:

   "Identify $A$ in the following chemical reaction" but the reaction itself is absent.

3. Since neither the reaction nor the answer options are provided, the identity of $A$ cannot be derived logically.

Comparison with stored answer

The stored correct answer is marked as A, but because the actual option contents are missing, I cannot verify whether that is correct.

Conclusion

Please provide the reaction scheme/image and the actual option structures/names so I can solve it properly step-by-step.