Answer:
3CO₂
Explanation:
x + 3H₂O + light ⟶ C₃H₆O₃ + 3O₂
This looks like a photosynthesis reaction, in which CO₂ acts as a source of carbon atoms for the product. Replace the x with CO₂.
CO₂ + 3H₂O + light ⟶ C₃H₆O₃ + 3O₂
You have three C atoms on the right, so you need three C atoms on the left. Put a 3 in front of CO₂.
3CO₂ + 3H₂O + light ⟶ C₃H₆O₃ + 3O₂
All atoms are now balanced
x = 3CO₂
