Is direct source of hydrogen NADH or water in photosynthesis?

In photosynthesis, the direct source of hydrogen is water (H₂O), not NADH. Water molecules are split during the light-dependent reactions, releasing oxygen and providing protons (hydrogen ions) and electrons. These protons are then used in the formation of NADPH, which carries the reduced form of NADP+ and is crucial for the Calvin cycle. Thus, water serves as the initial source of hydrogen.