The question asks for the number of $-\mathrm{CH_2}-$ (methylene) groups in the final product of a reaction sequence, but the actual reaction sequence/structure is missing from the prompt.

So, the product cannot be determined from the provided information alone.

What can be concluded?

Since the reaction scheme is absent, there is not enough data to derive the final structure and count the number of methylene groups.

Thus, I cannot independently verify whether the stored correct answer $0$ is right.

Comparison with stored answer

Because the reaction sequence is missing, I do not have a valid basis to agree with the stored answer.