In the question, they give you the initial number of moles of each substance present in the equilibrium. All of them should change by the same amount since the ratios are all 1:1, so lets say the change in the number of moles is x.
Therefore, the equilibrium concentrations are
(0.70–x) for CO2 and H2, and (0.30+x) for CO and H2O.
You know Kc is 1.44, and Kc = [products]/[reactants] yes? So pop those values in, and solve as a quadratic.
1.44= (0.30+x)^2 /(0.70-x)^2 etc, and solve for x.
It should give you x= 0.25, and so you substitute it back into the (0.70-x) for CO2 and H2, and (0.30+x) for CO and H2O.
i) The 30cm^3 is the excess oxygen that wasn't reacted with A.
ii) CO2 is the only other gas that is produced, so it should be quite obvious.
iii) Total volume of gas left after combustion = 40cm^3. If 30cm^3 is oxygen, then 10cm^3 should be CO2.
iv) Original volume of oxygen=50cm^3, and there is 30cm^3 of oxygen left. Therefore volume of oxygen reacted is 20cm^3
Basically they are referring to the number of each element in the monomers. They both have the same amount of each element, so you could say they're isomers, or they have the same molecular formula.
