This question involves stoichiometry question with a need to find a limiting reactant. You will need to have a balanced equation written before being able to calculate the answer.
Balanced equation and mole ratio:
If solid Aluminum and Oxygen gas react together to form Al2O2, the balanced equation would look like:
4Al (s) + 3O2 (g) --> 2Al2O2 (s)
with a mole ratio of 4:3:2 (4 mols of Al react with 3 mols of O to form 2 mols of 2Al2O3)
*We use this mole ratio to convert actual quantities of moles of what we have into how many moles we need to complete the reaction or how many moles we can make
Calculating Limiting Reactant:
If you have 1 mol of Al you need:
1 mol Al x 3 mol O2 = 0.75 mol O
4 mol Al
OR
If you have 3 mol O2 you need:
3 mol O2 x 4 mol Al = 4 mol Al
3 mol O2
Since we only have the 1 mol of Al (and not the 4 moles needed to react all 3 mol of O), Al is the limiting reactant and we'll use that to figure out how much Al2O3 we can make.
Calculating moles of Al2O3:
1 mol Al x 2 mol Al2O3 = 0.5 mol Al2O3
4 mol Al