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According to the chemiosmotic hypothesis, ATP is synthesised when protons

(a) are pumped into the stroma by NADP reductase Your answer
(b) combine with O₂ in the lumen Your answer
(c) move from the lumen to the stroma through CF₀ of ATP synthase Correct
(d) move from the stroma to the lumen through PS II Your answer

Your answer: Correct answer: (c)

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Explanation

Why (c) is correct

Protons move from the lumen (high concentration) to the stroma through the CF₀ channel of ATP synthase, and this drives ATP formation at CF₁.

Why the other options are wrong

(a) · your answer NADP reductase removes protons from the stroma; it does not pump them in.
(b) · your answer Protons do not combine with O₂ in the lumen.
(d) · your answer Protons do not move into the lumen through PS II to make ATP.

NCERT point: The gradient breaks down as protons flow back, and this energy is used for ATP synthesis.

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