Iron metal reacts with oxygen gas to produce iron(III) oxide. If you have 12.0 moles of iron, for complete reaction you need:

(HINT you need the balanced chemical reaction!)
A) 9.0 moles of O2 and produce 3.0 moles of Fe2O3
B) 9.0 moles of O2 and produce 6.0 moles of Fe2O3

1 answer

4Fe + 3O2>> 2Fe2O3

Looks like a 3:2 ratio to me.