To determine the limiting reagent when 3.1 mol of SO₂ react with 2.7 mol of O₂ according to the equation: 2SO₂(g) + O₂ --> 2SO₃(g), which of the following options provides the limiting reagent?
a. 2SO₂
b. O₂
c. 2SO₃
d. 3.1 mol of SO₂
e. 2.7 mol of O₂