Answer:
Carbon Dioxide
Explanation:
Let's see the reaction of Photosynthesis
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Where carbon dioxide and water are reactants and glucose and oxygen are products which means CO₂ and H₂O are taken from the environment and glucose is supplied to plants while oxygen is supplied back to the environment.
