Explanation
The photosystem II (PSII) is a protein complex involved in the first step of photosynthesis, which is the light-dependent reaction. PSII uses light energy to oxidize water, which releases electrons that are used to generate ATP and reduce NADP+ to NADPH.
The oxidation of water in PSII is facilitated by a cluster of four manganese (Mn) ions, known as the oxygen-evolving complex (OEC). The OEC undergoes a cycle of four oxidation states during the light-dependent reaction, resulting in the oxidation of two water molecules and the release of one molecule of molecular oxygen (O2).
Therefore, the correct answer is A: Manganese. Manganese plays an important role in the functioning of photosystem II by participating in the water-oxidizing reaction and providing electrons for the production of ATP and NADPH.
