The general equation of photosynthesis is:

6 CO2 + 6 H2O + light --> C6H12O6 +
6 O2.

Water molecules are also produced in the chemical stage of photosynthesis as the following complete equation reveals:

6 CO2 + 12 H2O + light --> C6H12O6 +
6 H2O + 6 O2

Water molecules are present in the reagent side as well in the product side of the equation. Pure mathematical simplification of stoichiometric coefficients however leads to elimination of water from the product side and it then seems that 6 molecules of molecular oxygen (O2), i.e., 12 atoms of oxygen, are made for each 6 molecules of water, i.e., 6 oxygen atoms, in the reagent side. Thus a false impression that 6 other oxygens come from carbon dioxide is created.   _{Your Comment}