Which gas is released as a byproduct of photosynthesis?

• A. Oxygen
• B. Carbon dioxide
• C. Nitrogen
• D. Hydrogen

Answer: (A)

Oxygen is the gas released as a byproduct of photosynthesis. In the light-dependent stage, water is split in the chloroplasts to provide electrons for the photosynthetic electron transport chain. This splitting releases oxygen gas, which escapes from the leaf. Carbon dioxide isn’t released; it’s taken up and used in the Calvin cycle to make sugars. Nitrogen gas and hydrogen gas aren’t produced in standard photosynthesis—the process uses hydrogen to form carriers like NADPH rather than emitting it as a separate gas.