The correct answer is option 3: 6 moles of oxygen gas.

When glucose undergoes complete combustion, it reacts with oxygen to produce carbon dioxide and water. The balanced chemical equation for this reaction is:

C6H12O6 + 6O2 -> 6CO2 + 6H2O

From the balanced equation, we can see that 1 mole of glucose (C6H12O6) reacts with 6 moles of oxygen gas (O2) to produce 6 moles of carbon dioxide (CO2) and 6 moles of water (H2O). Therefore, for every mole of glucose that is combusted, 6 moles of oxygen are required.

This balanced equation represents the stoichiometry of the reaction, meaning it shows the mole ratio of reactants and products. In this case, the mole ratio between glucose and oxygen is 1:6. This indicates that for every mole of glucose, 6 moles of oxygen gas must react.

Therefore, the correct answer is option 3: 6 moles of oxygen gas.