You are producing magnesium oxide by the reaction 2 mg + o 2 > 2 mgo . if you start out with 6 moles of magnesium, how many moles of oxygen will you need? how many moles of magnesium oxide will you produce?

2 Mg + O₂ --> 2 MgO

If we have 6 moles of magnesium, then we use the ratios from the balanced equation to find the moles of oxygen needed

MOLES O₂ = MOLES MG * (1 O₂ / 2 Mg) <--- we get this from equation
                    = 6 mol Mg * (1 O₂ / 2 Mg)
                    = 3 mol O₂ 
We need 3 moles of oxygen otherwise we will not have all 6 moles of magnesium react. This will product

MOLES MgO = MOLES MG * (2 MgO / 2 Mg)
                         = 6 mol Mg * (2 MgO / 2 Mg)
                         = 6 mol MgO
We will produce 6 moles of magnesium oxide