This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
All are free radicals except 
Select and explain. 
A. Superoxide, B. Hydrogen peroxide, C. peroxyl, D. Hydroperoxyl
B: Hydrogen peroxide
Answer: B: Hydrogen peroxide 
Explanation: Hydrogen peroxide is a reactive oxygen species but not a free radical because all electrons are paired. Clinical correlate: Chronic granulomatous disease also knows as Bridges-Good syndrome is due to deficiency of NADPH oxidase. The lysosomes are unable to produce hydrogen peroxide to kill the bacteria. The patients have increased susceptibility towards catalase-positive organisms. Reference: Harpers illustrated biochemistry 30th edition