The correct answer is b) light dependent reactions.
During the light-dependent reactions of photosynthesis, which occur in the thylakoid membranes of the chloroplasts, water molecules (H2O) are split through a process called photolysis. This reaction is driven by light energy absorbed by chlorophyll and other pigments.
As a result of this splitting, oxygen (O2) is produced as a byproduct and released into the atmosphere. Meanwhile, the energy harvested from this process is used to create ATP and NADPH, which are crucial for fueling the subsequent light-independent reactions (Calvin Cycle).
In contrast, light-independent reactions do not directly utilize water or produce oxygen; instead, they use the ATP and NADPH generated in the light-dependent reactions to convert carbon dioxide (CO2) into glucose.