The molar ratio between two compounds in a chemical equation refers to their relationship according to the stoichiometry of the reaction.
In this balanced chemical equation, there are 2 moles of C4H10 reacting with 13 moles of O2 producing 8 moles of CO2 and 10 moles of H2O.
The relation, or ratio, between oxygen and carbon dioxide is how much of oxygen there is to how much carbon dioxide.
Amount of O2 reacting: 13
Amount of CO2 being produced: 8
The ratio is:
D. 13:8