In the journey of electrons from photosystem II to photosystem I plastocyanin is reduced by:

Explanation

Plastocyanin is reduced when it accepts an electron from the cytochrome b6f complex, and this electron reduces the copper ion in plastocyanin from Cu²⁺ to Cu⁺. This process is essential for transferring electrons between photosystem II and photosystem I in the electron transport chain of photosynthesis.