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: Anaesthesia
Which anaesthetic gas has high propensity to accumulate in cavities? 
Select and explain. 
A. Halothane, B. Nitrous oxide, C. Ether, D. Sevoflurane
B: Nitrous oxide
Answer: B: Nitrous oxide 
Explanation: N2O can increase pressure significantly in closed air spaces (cavities) because for 1 mole of nitrogen removed 35 moles of N2O is replaced.