Unidirectional flow of electrons in photophosphorylation takes place in

The chlorophyll-$a$ molecule of Photosystem-$I$ absorbs light at a wavelength of $.........$ and the chlorophyll-$a$ molecule of Photosystem-$II$ absorbs light at a wavelength of $.........$ for maximum absorption.

The wavelength required for the Emerson enhancement effect is........

The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction?

Which photosystem is inactive in the red drop phenomenon?

When a chlorophyll molecule in $PS-II$ is excited,the electron released first passes into: