Tell if each is a synthesis reaction or a decomposition reaction.

1.) 2MgO ---> 2Mg + O₂

2.) 2Hg + O₂ ---> 2HgO

3.) C + O₂ ---> CO₂

4.) BaCl₂ ---> Ba + Cl₂

5) 2H₂O ---> 2H₂ + O₂​