The correct option is A An iron-sulphur protein
Photosystem- I (PS- I) is an integral membrane protein complex that absorbs solar energy and mediate electron transfer from plastocyanin to ferredoxin. Ferredoxin is the iron-containing sulphur protein, which is the first pigment that accepts electrons. The PS- I system comprises more than 110 cofactors, significantly more than photosystem- II.