Photolysis
Photolysis is the process of splitting water molecules using light energy, which occurs in Photosystem II during the Light-Dependent Reactions.
This reaction produces electrons, protons, and oxygen as byproducts. The electrons replenish those lost by Photosystem II, while the protons contribute to the Proton Gradient used to generate ATP.
The oxygen is released into the atmosphere as a vital byproduct of Photosynthesis.