Answer:
Water (H2O)
Explanation:
Light reactions of photosynthesis release oxygen as a by-product. In the presence of sunlight, photolysis of water molecules occurs. Splitting of two water molecules obtains four electrons, four protons, and molecular oxygen. The oxygen-evolving complex, also called the water-splitting complex is associated with photosystem II (PS II). Splitting of water occurs in the oxygen evolving complex and the released electrons are passed one at a time to the reaction center of PS II. Therefore, a water molecule serves as a source of oxygen released during photosynthesis.
