The source of O₂ liberated in photosynthesis is:

Explanation

The correct source of oxygen released during photosynthesis is water because it is split in the light-dependent reactions through a process called photolysis. When light energy strikes Photosystem II, water molecules are broken down into hydrogen ions, electrons, and oxygen. The oxygen is then released as a byproduct into the atmosphere. Photosynthetic enzymes only catalyse reactions but do not provide oxygen themselves. Carbohydrates are products of photosynthesis, not sources of oxygen, and carbon dioxide contributes carbon and oxygen atoms to glucose formation, but not to the oxygen gas that is released. Hence, only water serves as the true source of the oxygen liberated during photosynthesis.