Question

when an electron is emitted from photosystem ii, 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 ii is

carbon dioxide
atp
nadph
water

Explanation:

In photosynthesis, Photosystem II (PSII) uses light energy to split water molecules ($\ce{H_2O}$) into oxygen, protons, and electrons. When an electron is emitted from PSII, the electron needed to fill the "hole" comes from the oxidation of water. Carbon dioxide is used in the Calvin cycle (light - independent reactions), ATP and NADPH are products of the light - dependent reactions (ATP from photophosphorylation, NADPH from the electron transport chain after PSI), not the source of electrons for PSII.

Answer:

water (the option with "water" as the text)