Because for making one molecule of Glucose we need to fixed 6 molecule of CO2 so turn of C3 cycle will be 6 as we know for one C3 cycle we need 3 ATP and 2 NADH.H and for for 1 NADH2 we need 1 mole of water so,

12 NADH2 =12 H2O

Explanation:

Photosynthesis is the process in which plants, algae, and some bacteria convert sunlight into chemical energy stored in glucose molecules. The overall balanced equation for photosynthesis is:

6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

This equation shows that for every 6 molecules of carbon dioxide (CO2) and 12 molecules of water (H2O), one molecule of glucose (C6H12O6), 6 molecules of oxygen (O2), and 6 molecules of water (H2O) are produced.

Reasoning:

The reason why 6 molecules of H2O are not deducted from the 12 molecules of H2O on the left-hand side of the equation is because water molecules are not consumed or used up in the process of photosynthesis. Instead, water molecules are split during the light-dependent reactions of photosynthesis to provide electrons, protons, and oxygen.

During the light-dependent reactions, light energy is used to split water molecules into hydrogen ions (H+), electrons (e-), and oxygen molecules (O2). This process is known as photolysis. The oxygen molecules (O2) are released as a byproduct, while the hydrogen ions (H+) and electrons (e-) are used to generate ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) - the energy-carrying molecules required for the synthesis of glucose in the light-independent reactions.

Summary:

In summary, the equation for photosynthesis is balanced to represent the overall process accurately. The inclusion of 6 molecules of water (H2O) on the product side of the equation (C6H12O6 + 6O2 + 6H2O) accounts for the release of oxygen molecules (O2) during the light-dependent reactions and the utilization of water molecules in the production of ATP and NADPH. Therefore, the equation correctly represents the conservation of matter in photosynthesis.