In order to get HgO you would need 2Hg+1O2=2HgO. Since oxygen is diatomic you need two when it stands alone causing you to need two mercuries to balance out the reactants and the product I hope this helps
The answer is theory because it says if and that means theory
It was most likely either weathering or tectonic plates moving away from each other. More likely tectonic plates
Do you mean h=7.0+10? If so your answer is 70.