The correct option is A 2
Oxidation of one molecule of FADH2 gives rise to 2 molecules of ATP.
During Krebs cycle, when succinate is oxidized to fumarate, 2 protons and 2 electrons are released. These are taken by FAD+ and FADH2 is formed. This FADH2 undergoes oxidation and releases electrons which pass through the electron transport chain. The energy of these electrons is utilised to pump protons into the intermembrane space of mitochondria. This creates a proton gradient and helps to generate ATP.