To solve this problem, we need to analyze the statements regarding ATP synthesis through chemiosmosis and identify which one is not true. Let's examine each option:$\newline \bullet$Option 1: Breakdown of proton gradient$\newline$ - During chemiosmosis, the energy for ATP synthesis is derived from the breakdown of the proton gradient across the membrane.$\newline$ - This is a true statement as the movement of protons back across the membrane through ATP synthase drives ATP production.$\newline \bullet$Option 2: Breakdown of electron gradient$\newline$ - There is no electron gradient involved in chemiosmosis. Instead, electrons are transferred through the electron transport chain, which helps establish the proton gradient.$\newline$ - This statement is not true as chemiosmosis does not involve a breakdown of an electron gradient.$\newline \bullet$Option 3: Movement of protons across the membrane to the stroma$\newline$ - In chloroplasts, protons move from the thylakoid lumen to the stroma through ATP synthase, facilitating ATP synthesis.$\newline$ - This is a true statement.$\newline \bullet$Option 4: Reduction of NADP to NADPH on the stroma side of the membrane$\newline$ - The reduction of NADP to NADPH occurs on the stroma side of the thylakoid membrane, which is part of the light reactions in photosynthesis.$\newline$ - This is a true statement.$\newline$Based on the analysis, the statement that is not true regarding ATP synthesis through chemiosmosis is:$\newline$Option 2: Breakdown of electron gradient.$\newline$Therefore, the correct answer is Option 2.