The cellular respiration of glucose (C₆H₁₂O₆) can be summarized by the following chemical equation:
\[ 6 \text{O}_2 + \text{C}6\text{H}{12}\text{O}_6 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{energy} \]
From the equation, we can see that one glucose molecule requires 6 oxygen molecules for complete respiration. Therefore, for two glucose molecules, you would need:
\[ 2 \times 6 \text{O}_2 = 12 \text{O}_2 \]
Thus, the answer is 12 oxygen molecules.