What type of reaction is most likely to occur when barium reacts with fluorine? combustion synthesis decomposition single replacement?

Answer is: synthesis.

Chemical reaction: Ba + F₂ → BaF₂.

Synthesis is type of reaction where two or more compounds (in this reaction barium and fluorine) react to form one product (in this reaction BaF₂).

BaF₂ - barium fluoride, salt, white cubic crystals, soluble in methanol and ethanol.

The type of reaction is synthesis since it involve the transfer of the electron between fluorine and barium. Barium has two valence electrons which it need to lose to become stable while chlorine require only one electron to be stable. Barium therefore transfer the two electron to the two fluorine atoms

Ba (s) + F2 (g) - - > Baf2 (s)