Choose the condition that must be specified in order to liquify CO₂ (triple point for CO₂ is -57°C and 5.2 atm).

A. Pressure must be kept below 5.2 atm

B. Temperature must be kept above -57°C

C. Pressure must be kept below 5.2 atm. and temperature must be kept above 57°C

D. Pressure and temperature must be kept below 5.2 atm. and -57°C respectively

Answer: Option D

Solution(By Examveda Team)

If we see the typical $$p-T$$  plot any substance below the triple point we have only sublimation zone that means no liquefaction is not possible if we still decrease the pressure hence always the pressure should be greater than triple point pressure and the value of temperature depends on the pressure at which the substance is present.