This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Reperfusion injury is caused by: 
Select and explain. 
A. Vitamin E, B. Superoxide ion, C. Calcium ion, D. Magnesium ion
B: Superoxide ion
Answer: B: Superoxide ion 
Explanation: B i.e. Superoxide ion- Xanthine oxidase increases oxidative stress by generating superoxide free radiclesQ- Ischemic reperfusion injury is caused by reactive oxygen species (ROS)/free radical or pro oxidant like superoxide ionQAntioxidants blocking free radical formation include vitamin A (Beta carotene), C and E; superoxide dismutase, catalase and selenium containing glutathione peroxidase enzymes; ceruloplasmin, transferrin, ferritin, and lactoferrin transpo proteins etc.