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
Most stable radio-isotope among the following – 
Select and explain. 
A. O –18, B. C – 14, C. P – 32, D. I – 125
A: O –18
Answer: A: O –18 
Explanation: O-16,O-17, O -18 are stable radioisotopes of oxygen.
C-12, C-13, are stable radioisotopes of carbon (not C-14).
P-31, is stable radioisotopes of phosphorus (not P-32).
1-125 is radioactive form of iodine (not stable).