Answer:
The correct answer is NADPH.
Photo-system I absorbs maximum photons at the wavelength of 700 nm.
It uses this energy to transfer the electron (received from photo-system II) to NADP⁺ to reduce it to NADPH.
Once, the reaction centre of PS I or P₇₀₀ gets excited, it transfer the high energy electron to the ferrodoxin (Fd) via cluster of iron and sulphur protein (4Fe-4S).
Reduced ferrodoxin then transfer the electron to NADP⁺ to reduce it to NADPH with the help of flavoprotein (ferrodoxin-NADP⁺ reductase).
NADPH is then used in Calvin cycle or light-independent phase of the photosynthesis in order to fix carbon to produce sugar or food.