The minimum number of moles of O₂ required for complete combustion of 1 mole of propane and 2 moles of butane is

C? H? + 5O? → 3CO? + 4H? O
C? H? + (13/2)O? → 4CO? + 5H? O
∴ 2 mol C? H? is given
∴ 13 mol O? is required for combustion of Butane
∴ Total mol of O? = 5 + 13 = 18