During light reactions, atp is produced when hydrogen ions move:
a. down their concentration from the stroma into the thylakoid space
b. against their concentration gradient from the stroma to the thylakoid space
c. down their concentration gradient from the thylakoid space into the stroma
d. against their concentration gradient from the thylakoid into the stroma

The correct answer will be option-C.

Explanation:

Light-dependent reactions are the reaction of photosynthesis which takes place in the presence of light.

During light reaction, ATP and NADPH intermediates are produced which are utilized during the light-independent reaction. The main reactions that take place during light reactions are photolysis of water and ATP synthesis due to the electron transport chain.

Electron transport chain generates electrochemical gradient across the thylakoid membrane sue to the accumulation of protons in the thylakoid lumen and fewer protons in the stroma of the chloroplast.

This causes the osmotic movement of protons down their concentration gradient through ATP synthase. The movement if hydrogen ions take place from thylakoid lumen to stroma forming ATP molecules.

Thus, Option-C is the correct answer.

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