This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anaesthesia
Critical temperature for liquid nitrogen is 
Select and explain. 
A. 36.5degC, B. -20degC, C. -147degC, D. -242degC
C: -147degC
Answer: C: -147degC 
Explanation: Critical temperature (Tc) of substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied (Note: Below critical temperature a substance can exist as a liquid or gas depending on pressure).Critical temperature of N2 is-146.9degC; that means N2 can b3e liquefied below -146.9degC - So, liquid nitrogen must be stored below -146.9degC(Refer: Morgan and Mikhail's Clinical Anaesthesiology, 5th edition, pg no 11 -12)