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
Which of the following is not a free radical, but it is a reactive oxygen species? 
Select and explain. 
A. Hydroxyradical, B. Hydrogen peroxide, C. Superoxide radical, D. Both 1 & 2
B: Hydrogen peroxide
Answer: B: Hydrogen peroxide 
Explanation: Most powerful oxygen free radical is Hydroxyradical.
Least powerful Reactive Oxygen species(ROS) is Hydrogen peroxide.
Precursor of all Reactive Oxygen species is Superoxide radical.
H2O2 is not a free radical,  but a ROS.

Reference- Review of biochemistry Pg-411