From the stoichiometry, 2 moles of SO₂ react with 1 mole of O₂. To react with 5.0 moles of SO₂, we would need 2.5 moles of O₂. Since we only have 1.0 mole of O₂, O₂ is the limiting reagent. 1 mole of O₂ will produce 2 moles of H₂SO₄.