The desired equation is;
2CO2vol.+O21vol.→2CO22vol.
1 vol. of O2 reacts with 2 vol. of CO
or 1 lime of O2 reacts with 2 litre of CO
Thus, 1 litre of CO remains unreacted.
1 vol. of O2 produces CO2=2vol.
Or 1 litre of O2 will produce CO2=2litre
Thus, gaseous mixture after the reaction consists Volume of CO=1litre
Volume of CO2=2litre