Question

Why is dry ice stored under high pressure?

Answer 1

 dry ice stored under high pressure because- 
carbon shift's to its solid phase in the extreme temperatures of −78.5 °C.to keep it stable like that for a longer time , we need to exert and store it in high pressures and obviously low temp. this helps in not letting it escape from solid phase. 

Answer 2

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Solid CO² get converted directly to gasesous state on decrease of pressure to 1 atomsphere without come into liquid state . This is the reason that solid CO² is also known as dry ice .