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: Radiology
Longest half life is seen in 
Select and explain. 
A. Radon, B. Radium, C. Uranium, D. Cobalt
B: Radium
Answer: B: Radium 
Explanation: B i.e. Radium