C is the correct answer (CaF2) (sorry dont have subscript)
Explanation: synthesis reaction forms a compound and calcium reacting with fluorine produces Calcium Fluoride (CaF2) chemical name
I just answered your other question and wrote all the definitions of the terms. I would say this is probably refering to Fusion because you are fusing together more nuclei into one nucleus. Fusion= bringing separate things into one entity.
The answer is C I got it right so hope it helped ;)