Which of the following is not a reason of H⁺ gradient development in chloroplast?

The oxidation of NADH+H⁺ and FADH₂ is not a reason for the development of a proton (H⁺) gradient in chloroplasts. 

During photosynthesis, the splitting of water molecules occurs on the inner side of the thylakoid membrane in the chloroplasts. As a result of this process, protons or hydrogen ions are generated and accumulate within the lumen of the thylakoids. As electrons move through the photosystems, protons are transported across the membrane. This is due to the fact that the primary electron acceptor, located on the outer side of the membrane, transfers its electron not to an electron carrier but to an H carrier. This molecule, while transporting an electron, removes a proton from the stroma and, upon passing its electron to the inner side of the membrane to an electron carrier, releases the proton into the lumen.

On the stroma side of the membrane, the NADP reductase enzyme is located. This enzyme plays a crucial role in the reduction of NADP+ to NADPH+ H+ during photosynthesis. It requires both electrons, which come from the electron acceptor of Photosystem I, and protons to carry out this reduction. These protons are also sourced from the stroma.