What gas is a byproduct of photosynthesis?

During the process of photosynthesis, plants convert carbon dioxide and water into glucose and oxygen, using sunlight as the energy source. The overall chemical equation for photosynthesis illustrates this process, showing that oxygen is produced as a byproduct. While carbon dioxide is one of the reactants used in photosynthesis, it is not a byproduct. Nitrogen and hydrogen are not directly involved in the photosynthetic process in the same way, making them irrelevant to the outputs generated by this fundamental biological process. Therefore, oxygen is the correct answer as it is released into the atmosphere and is vital for the respiration of most living organisms.