Answer:
The number of oxygen atoms in each oxygen molecule
Step-by-step explanation:
The subscript in 6O₂ represents the number of oxygen atoms in each oxygen molecule.
A is wrong. The subscript tells you nothing about the atomic weight of oxygen.
B is wrong. The 6 tells you how many molecules of O₂ are produced with each molecule of glucose.
D is wrong. The 6 tells you the number of oxygen atoms needed to balance the equation.