This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anaesthesia, Subject name: Anaesthesia
Gas stored in liquid form is 
Select and explain. 
A. Carbon dioxide, B. Nitrous oxide, C. Cyclopropane, D. Oxygen
B: Nitrous oxide
Answer: B: Nitrous oxide 
Explanation: N20 is stored in blue steel cylinders as a colorless liquid under 745 psi pressure and is in equilibrium with the gas phase (approximately 50 atmospheres at room temperature). The tank maintains that pressure until it is empty.