The light reactions require the cooperation of 2 photosystems to power linear electron flow from h2o to nadp+.?
separate each item into one of the three categories, photosystem ii (ps ii) only, photosystem i (ps i) only, or both ps ii and ps i.
1. reduction of nadp+.
2. reduction of primary electron acceptor.
3. oxidation of water.
4. light absorbtion.
5. reduction of electron transport chain between the two photosystems.
6. oxidation of electron transport chain between the two photosystems.

Only Photosystem I  - 1, 5, 6

Only photosystem II - 3, 2

Both Photosystem I and II   - 4

Explanation:

Only Photosystem I  

a) Reduction of NADP+ -  uses light energy to convert NADP+ to NADPH2

b)  Reduction of electron transport chain between the two photosystems

c) Oxidation of electron transport chain between the two photosystems.

Only photosystem II

a)  Oxidation of water - here the absorbed light energy is used to dissociate of water molecules to produces protons (H+) and O2 along with free ions

b)Reduction of primary electron acceptor - An electron is taken by pheophytin which is a primary electron acceptor molecule that is  located within photosystem II and hence it get reduced.

Both Photosystem I and II  

a) Light is absorbed in both photosystem I and II. While in photosystem I, light waves of large wavelength i.e 700 nm are absorbed, in photosystem II light waves of short wavelength of i.e 680 nm are absorbed.

I believe your answer would be A