The correct answer is PS II (Photosystem II).
During the process of photosynthesis, specifically in the light-dependent reactions, Photosystem II plays a crucial role in generating oxygen. This occurs when water molecules are split in a process known as photolysis, which takes place in the thylakoid membranes of chloroplasts. When light energy is absorbed by PS II, it energizes electrons, leading to the breakdown of water into oxygen, protons, and electrons.
The oxygen produced as a byproduct of this reaction is then released into the atmosphere, making photosynthesis vital for maintaining levels of atmospheric oxygen, which is essential for most living organisms on Earth.