Oxygen is released during:

Explanation

Oxygen is released during photolysis, which occurs in the light-dependent reactions of photosynthesis. In this process, light energy absorbed by photosystem II splits water molecules into oxygen, protons, and electrons. The oxygen produced during photolysis is released into the atmosphere as a by-product, while the electrons and protons are used to generate ATP and NADPH for the Calvin cycle. Phosphorylation is incorrect because it refers to the production of ATP, not the splitting of water or the release of oxygen. The electron transport chain is incorrect because it transfers electrons through a series of carriers but does not produce oxygen. Carboxylation is also incorrect because it involves the fixation of carbon dioxide in the Calvin cycle, not the generation of oxygen.