How many moles of Magnesium must react with excess Oxygen to produce 80g of Magnesium oxide?

This question looks at the reaction:
Magnesium + Oxygen goes to Magnesium Oxide
Mg + O --> MgO
The first step is to calculate the moles of MgO produced using the mass in the question and the relative formula mass of MgO.
The RFM of MgO can be found using a periodic table. The atomic mass of Mg is 24 and the atomic mass of Oxygen is 16. Therefore the RFM of MgO is 24+16=40.
Now we can find the moles of MgO using the formula: moles = mass / RFM
moles MgO = 80 / 40
moles MgO = 2
Looking back to the equation for the reaction:
Mg + O --> MgO
We can see that one unit of Mg goes to produce one unit of MgO.
Therefore to produce 2 moles of MgO, we must use 2 moles of Mg.