What temperature is necessary to liquefy O2 at 1 atm pressure?

a. ?118.8° C
b. ?181.1° F
c. ?463.3° F
d. ?183.0° C

ANS: D
Liquid O2 is produced by separating it from a liquefied air mixture at a temperature below its boiling point (−183° C or −297° F). After it is separated from air, the O2 must be maintained as a liquid by being stored in insulated containers below its boiling point. As long as the temperature does not exceed –183° C, the O2 will remain liquid at atmospheric pressure. If higher tempera-tures are needed, higher pressures must be used. If at any time the liquid O2 exceeds its critical temperature of –118.8° C, it will convert immediately to a gas.