Final answer:
H2O is not a reactant in Phase 1 of Photosynthesis.
Step-by-step explanation:
In Phase 1 of photosynthesis, also known as the light-dependent reactions, water, carbon dioxide, sunlight, ATP, and NADPH are involved as reactants. These reactants are used to generate oxygen, ATP, and NADPH as products. Therefore, the answer to the question is option D. H2O, which is not a reactant in Phase 1 of photosynthesis.