First, 55 g of Hg is 3.65 moles because one mole of Hg has a molar mass of 200.59
Then, the mole ratio of Hg to CaO is 8:4 or 2:1. SO we divide 3.65 by 2 to get 1.82 moles of CaO
This is the same as 102.06 grams because one mole of CaO has a molar mass of 56.0774
Hope this helps!
Look at the periodic table (Boron has 3) and count up from there
It's a because if you add them together you till get 1.40
