The correct option is D PS I and PS II are named in the sequence of their discovery.
Photosynthesis involves a variety of pigments which play an active role in trapping the solar wavelengths. The pigments are organised into two discrete photochemical light harvesting
complexes within the Photosystem I (PS I) and Photosystem II (PS II).
PS I and PS II are named in the sequence of their discovery, and not in the sequence in which they function during the light reaction.
When the two photosystems work in a series, first PS II and then the PS I, a process called non-cyclic photo-phosphorylation occurs. Splitting of water occurs at PS II during this process.
When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation is called cyclic photophosphorylation.