This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
Which of the following has the maximum ionization potential 
Select and explain. 
A. Electron, B. Helium ion, C. Proton, D. Gamma photon
B: Helium ion
Answer: B: Helium ion 
Explanation: (Ref: Farr&;s physics for medical imaging 2e,23 )