to which substance does ferredoxin transfer an electron?\no photosystem i\no photosystem ii\no nadp+\no nadph

Brief Explanations:

In the light - reactions of photosynthesis, ferredoxin transfers an electron to $NADP^{+}$ to form NADPH. Ferredoxin is the last electron carrier in the electron - transport chain of the light reactions. It donates its electron to $NADP^{+}$, which is reduced to NADPH. Photosystem I and II are involved in the initial steps of the electron - transport chain and do not receive electrons from ferredoxin in this context.

Answer:

C. $NADP^{+}$