For the cellular respiration of one glucose molecule (C6H12O6), the reaction is:
\[ \text{C6H12O6} + 6 \text{O2} \rightarrow 6 \text{CO2} + 6 \text{H2O} + \text{energy} \]
This means that 6 O2 molecules are required for one glucose molecule. Therefore, for two glucose molecules, you would need:
\[ 2 \times 6 \text{O2} = 12 \text{O2} \]
The correct answer is 12 O2 molecules.