The respective oxidation reactions are,
2H2+O2→2H2O
CH4+2O2→CO2+2H2O
2CO+O2→2CO2
C2H2+52O2→2CO2+H2O
From the given percentage of gases,
Here volume of C2H2=0.02 m3
volume of O2 required = 0.05 m3
volume of CO=0.08 m3
volume of O2 required = 0.04 m3
volume of CH4=0.35 m3
volume of O2 required = 0.7 m3
Volume of H2=0.50 m3
volume of O2 required = 0.25 m3
Hence the total required volume of oxygen for the combustion of given gas mixture =1.04 m3
Hence, volume of air required =1.04×10020.8=5 m3