Answer is: 6 molecules of oxygen.
First, write down reaction for aerobic respiration:
C₆H₁₂O₆ (glucose) + 6O₆ (molecule of oxygen) → 6CO₂ (carbon-dioxide) + 6H₂O (water).
Reaction shows that one molecule of glucose react with six molecules of oxygen.
Aerobic respiration requires oxygen to create energy.
