Final answer:
The oxygen produced during photosynthesis comes from water, with the process converting water and carbon dioxide into glucose and oxygen, utilizing sunlight.
Step-by-step explanation:
Plants produce oxygen when they photosynthesize. The oxygen comes from the water (H2O) that is used in the photosynthesis process. During photosynthesis, in the presence of sunlight, carbon dioxide (CO2) and water combine to create glucose (C6H12O6), a carbohydrate, and oxygen (O2). This reaction can be summarized as:
6CO2(g) + 6H2O(l) + light energy → C6H12O6 + 6O2(g)
Here, oxygen is actually a waste product as the primary role of photosynthesis is to create glucose, which serves as a food source for plants.