In order to find the number moles of oxygen needed to produce 12 moles of carbon dioxide, we need to write out an equation for the chemical reaction. From that, we will get the stoichiometric ratio between oxygen and carbon dioxide to complete our calculation.
The chemical reaction to produce carbon dioxide from oxygen is:
1x O2 + 1x C => 1x CO2
The stoichiometric ratio between oxygen and carbon dioxide is 1:1. So 12 moles of Oxygen are needed.