There are 0.4 moles of O2
and 0.6 moles of CO, and we know that 2CO + O2 à 2CO2.
Using
the above equation, we can say that 0.6 moles of CO react with 0.3 moles of O2 to create 0.6 moles of CO2
Therefore,
in the end there will be .6 moles of CO2 and .1 moles of O2. There will be no CO left as it will be completely
consumed in the reaction.
The
mole fraction of O2 in the mixture is .1/(.6+.1) = 0.143