Critical temperature for liquid nitrogen is
36.5degC
-20degC
-147degC
-242degC
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)
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