The by-product of photosynthesis is :

Explanation

Photosynthesis is the process in which the green parts of plants absorb light energy from the sun and, using carbon dioxide (CO₂) taken from the air and water (H₂O) absorbed from the soil, prepare carbohydrates and release oxygen (O₂) as a secondary product or by-product. The overall process of photosynthesis can be represented by the following reaction— Light 6CO₂ + 12H₂O —> Chlorophyll → C₆H₁₂O₆ + 6H₂O + 6O₂