This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
Which one among the following is not an antioxidant? 
Select and explain. 
A. Zinc, B. Selenium, C. Copper, D. Iron
D: Iron
Answer: D: Iron 
Explanation: Zn plays a role as anti-oxidant as it binds with SH group of biomolecules protecting them from oxidation. Also it increases the activation of anti-oxidant propeies. Action of Se is complementary to Vitamin E, constituent of Glutathione Peroxidase and Selenocysteine. Cu has role as anti-oxidant as it is present as a constituent in Cu/Zn SOD and Ceruloplasmin. Biological Functions of Iron: Transpo and storage of O2 (Hb and Mb) and CO2. In ETC as component of cytochromes. Co-factor for many enzymes e.g. Catalase, Peroxidase, Tryptophan Pyrrolase. Role in phagocytosis (Peroxidase contains iron required for Phagocytosis).