Which of the following is not responsible for the generation of Reactive Oxygen Species?
ROS are produced normally in small amounts in all cells during the reduction-oxidation (redox) reactions that occur during mitochondrial respiration and energy generation.
Free radical-mediated cell injury is seen in many circumstances, including chemical and radiation injury, hypoxia, cellular aging, tissue injury caused by inflammatory cells, and ischemia-reperfusion injury. In all these cases, cell death may be by necrosis, apoptosis, or the mixed pattern of necroptosis.
The ROS are generated in the phagosomes and phagolysosomes of leukocytes by a process that is similar to mitochondrial respiration and is called the respiratory burst (or oxidative burst).
In the presence of metals, such as Fe2+, H2O2 is converted to the highly reactive hydroxyl radical by the Fenton reaction.​

Robin’s Textbook of pathology 10th ed Page 43-44
Reperfusion of ischemic tissues
Mitochondrial respiration and energy generation
Presence of Fe+++ ions
Respiratory burst