In his experiment that led to the discovery of oxygen, Priestley heated some red mercuric oxide and caused it to break apart. The chemical reaction is: HgO (s) → Hg (s) + O2 (g)

Is this chemical reaction balanced? Why or why not?

1 No, because the number of oxygen atoms is different on both sides.

2 No, because the number of both mercury and oxygen atoms is different on both sides.

3 Yes, because the number of both mercury and oxygen atoms is the same on both sides.

4 Yes, because the number of mercury atoms is the same on both sides.