Oxygen liberated during photosynthesis comes from

Water, during the light-dependent reactions.

Explanation:

During the light-dependent reactions, a photon (particle of energy) from the Sun strikes the pigment molecules in Photosystem I in the thylakoids of chloroplasts. The pigment molecules pass the energy around until it strikes a pair of electrons located where Chlorophyl A is. One electron is "bounced" to the primary electron acceptor. But now it's gone. What replaces it?

The answer is in water. However, water not only provides replacement electrons; it also provides oxygen. When two oxygen atoms accumulate, they are released as a pair. Thus the answer is water. Hope u found this helpful! :)

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