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: Ophthalmology
Pneumoretinopexy is an outpatient procedure in which retinal detachmentis sealed with air insufflation. Which of the follov gas is used in pneu-etitiopexy? 
Select and explain. 
A. Sulfur hexafluoride, B. Carbon dioxide, C. Nitrous oxide, D. Oxygen
A: Sulfur hexafluoride
Answer: A: Sulfur hexafluoride 
Explanation: Ans. a. Sulfur hexafluoride