The question asks which reaction changes the hybridisation of the underlined atom, but the actual reactions/options A, B, C, D are missing in the prompt.

So, the problem as currently provided is incomplete, and it is not possible to determine which option is correct from the available information.

What is needed

To solve this, I need the actual reactions in options A, B, C, and D, along with the indication of the underlined atom in each reaction.

Then the method would be:

1. Identify the underlined atom in reactant and product.
2. Determine its hybridisation before reaction.
3. Determine its hybridisation after reaction.
4. Check whether it changes, e.g.
   • $sp \to sp^2$
   • $sp^2 \to sp^3$
   • $sp^3 \to sp^2$, etc.
5. The option showing a change would be the answer.

Present conclusion

Since the options are absent, no valid derivation can be made from the given data.