In the context of releasing oxygen to the atmosphere, only one of the processes you've listed does this: photosynthesis. Let me explain it in a simple way.
Photosynthesis is a process carried out by plants, some bacteria, and algae. These organisms use sunlight, carbon dioxide, and water to create their food, which is a form of sugar. As a byproduct, they release oxygen into the atmosphere. During this process, chlorophyll, the green pigment in plant cells, captures light energy, and helps convert it into chemical energy.
None of the other processes release oxygen:
- Respiration is a process in which living organisms, including plants and animals, take in oxygen and use it to convert glucose into energy, producing carbon dioxide and water as byproducts.
- Combustion involves burning substances, typically in the presence of oxygen, usually resulting in the production of carbon dioxide, water, and energy (heat and light). It does not release oxygen; rather, it consumes oxygen.
- Decomposition is the breakdown of dead organic matter by microorganisms. During this process, organic matter is converted back into carbon dioxide, methane, and other compounds, but it does not release oxygen.
So, the process that releases oxygen into the atmosphere is photosynthesis.