The first reaction is:
6CO2+12H2OChlorophyll,sunlight−−−−−−−−−−−−−−−−−−→6O2+C6H12O6+6H2O.
There are 12 water molecules at the reactant side and 6 water molecules at the product side.
The second reaction is:
6CO2+6H2OChlorophyll,sunlight−−−−−−−−−−−−−−−−−−→C6H12O6+6O2.
There are 6 water molecules at the reactant side.
If we subtract 6 water molecules at both the sides in the first reaction, we can get the second reaction.
Therefore, both the reactions are equally correct.