The oxygen liberated during photosynthesis comes from water (H₂O). In the process of photosynthesis, water molecules are split, a process called photolysis, releasing oxygen as a byproduct. This occurs during the light-dependent reactions of photosynthesis.
Here’s why the other options are incorrect:
Chlorophyll:
Chlorophyll is a pigment that absorbs light energy, which is then used to power the photosynthetic reactions. It’s essential for photosynthesis but doesn’t directly release oxygen.
Carbon dioxide (CO₂):
Carbon dioxide is a reactant in photosynthesis, meaning it’s used up in the process. The carbon atoms in CO₂ are incorporated into glucose, not the source of oxygen.
Glucose:
Glucose is the sugar produced as a product of photosynthesis. It’s not a source of oxygen, and oxygen is released as a byproduct of the process.