During the light dependent reaction, the hydrogen ions go down their concentration from producing atp in the process.
a. the stroma into the thylakoid lumen
b. the thylakoid lumen into the stroma
c. across the inner membrane into the stroma
d. the stroma across the inner membrane

b. The thylakoid lumen into the stroma

Explanation:

During light reaction of photosynthesis, when electrons which have high energy travel across electron transport chain some energy is released by them. This energy causes some H+ from stroma to move into thylakoid lumen. Due to this, H+ concentration becomes more in lumen as compared to stroma. Soon after that because of concentration gradient, these H+ then start moving from high concentration to low concentration i.e. from thylakoid lumen to stroma. There are some reverse pumps i.e. ATP synthase located in the thylakoid membrane which are responsible for generating energy in the form of ATP from the movement of H+. From the movement of 3 H+ , 1 ATP is generated.

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