The gas that green plants release during photosynthesis is oxygen (O₂). Photosynthesis is the process by which plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose. During this process, plants take in carbon dioxide (CO₂) from the atmosphere and water (H₂O) from the soil, using sunlight to convert these substances into glucose and oxygen. The oxygen produced is released into the air, which plays a vital role in maintaining atmospheric balance and supporting life for aerobic organisms, including humans.