when an electron is admitted from photosystem to it does not return the photosystem cannot trap any more light energy until the “hole” in the photosystem is filled with another electron the source of the electron that fills the “hole” in photosystem 2 is

Answer 1

water. When water molecules are split in the process of photosynthesis, they release electrons which are used to fill the "hole" in photosystem 2. This process releases oxygen as a byproduct.