Which gas is a byproduct of photosynthesis?

During photosynthesis, plants, algae, and some bacteria convert carbon dioxide and water into glucose and oxygen using sunlight as an energy source. The overall process involves the absorption of carbon dioxide from the atmosphere and the uptake of water from the soil. As a result, oxygen is released as a byproduct of this conversion. This oxygen is then expelled into the atmosphere, where it becomes available for use by other living organisms, such as animals and humans, in the process of respiration. Thus, oxygen is the definitive byproduct of photosynthesis, which is why it is the correct answer in this context.