Hello, thank you for taking the time to post your question!
The first step on solving this question is to get a balanced chemical equation for the combustion of isopropanol. That would be
2 𝐶3𝐻7𝑂𝐻 + 9𝑂2 → 6𝐶𝑂2 + 8𝐻2𝑂
Next then we want to find the moles of CO2 produced by taking the amount given and then dividing by the molar mass of CO2
(200.8 g CO2) / (44.01 g/mol) = 4.562 mol
Finally then you can convert that over into moles of Oxygen by multiplying by the ratio of the coefficients:
4.562 mol x (9 mol O2 / 6 mol CO2)
=6.843 mol O2
So the moles of oxygen used up in this combustion reaction is 6.843 moles.
I hope that helps! Feel free to shoot me a message if you have any questions beyond that :)
