Hydrogen ions are important in the light-dependent reactions of photosynthesis because they produce a
difference in charge across the thylakoid membrane that allows
a. the production of ATP.
b. the release of water molecules.
c. light to enter the chloroplast.
d. the conversion of 3-carbon molecules into higher-energy forms.

Photosynthesis is type of biosynthesis that produces glucose from the reactants sunlight, carbon dioxide and water. It happens in two phases of the chloroplast, the light-dependent and light-independent reactions. In a light reaction that stimulates photosystems, pigments such as chlorophyll absorb light energy at specific wavelengths. Here,

Light energy stimulates photosystem complexes formed from chlorophyll. Photosystem II then absorbs and transfers light to a reaction core.
Water undergoes hydrolysis or splitting to yield an electron, a proton (H+) and oxygen.
energy is passed along the electron transport chain, where it forms builds up H+ and an electrochemical gradient in the thylakoid space
These protons pass through the ATPase enzyme embedded within the membrane, into the stroma, generating ATP from ADP.
NADPH is generated from NADP+