The question asks: "Choose the reaction which is not possible", but the actual reactions for options A, B, C, and D are missing from the prompt.

So, the problem is incomplete: without the reaction schemes, it is not possible to chemically evaluate which option is feasible or not.

Step 1: Identify the issue

For a question of this type in organic chemistry, each option must contain a reaction or transformation. Here, the options are shown only as:

• A:
• B:
• C:
• D:

with no reactants, reagents, or products.

Step 2: Can the answer be derived from chemistry alone?

No. Since no reaction details are given, there is no basis to test possibilities such as:

1. oxidation/reduction feasibility,
2. nucleophilic addition/elimination,
3. decarboxylation behavior,
4. aldehyde/ketone/carboxylic acid interconversion,
5. reagent compatibility.

Step 3: Compare with stored answer

The stored correct answer is D, but because the options themselves are absent, I cannot independently verify whether D is correct.

Therefore, I do not have enough information to agree confidently with the stored answer.

Conclusion

The question is incomplete, so the reaction that is not possible cannot be determined from the provided data.