J.R. S. answered 04/23/19
Ph.D. University Professor with 10+ years Tutoring Experience
Find moles of O2 and then from the balanced equation find moles and mass of Al.
PV = nRT
n = PV/RT = (1 atm)(2.00 L)/(0.0821 Latm/Kmol)(273 K)
n = moles O2 = 0.0892 moles
moles Al = 0.0892 moles O2 x 4 moles Al/3 moles O2 = 0.119 moles Al
mass Al = 0.119 moles x 26.98 g/mole = 3.21 g of Al