Question

Why twelve moles of water is used as a substrate in photosynthesis equation

Answer 1

Because of any thing

Answer 2

equation of photosynthesis is
6CO2 + 12H2O -------------> C6H12O6 + 6O2 + 6H2O
we take 12 moles of water rather than 6 cause water may sometimes evaporate due to high temparature and if we provide only 6 moles there might be a deficiency in water for photosynthesis. the excess water comes out through transpiration.