Final answer:
The process when ultraviolet light creates free oxygen by splitting water molecules in the atmosphere is called photochemical dissociation. This differs from photosynthesis, which also produces oxygen but through a biological process in green plants.
Step-by-step explanation:
The process called when free oxygen is produced in the atmosphere by ultraviolet light splitting a water molecule is known as photochemical dissociation. This is different from photosynthesis, which is the process by which green plants and some other organisms use sunlight to synthesize foods with the production of oxygen as a by-product. In the atmosphere, the high-energy ultraviolet radiation can break down water (H₂O) and nitrous oxide to release oxygen molecules into the air. This process is critical as it contributes to the Earth's protective ozone layer. Through photosynthesis, which captures light energy from the sun, water is also converted into oxygen, releasing it into the atmosphere where it supports life.