# Using the phase diagram for CO_2, what phase is carbon dioxide in at -20 C and 1 atm pressure?

A phase diagram for ${\text{CO}}_{2}$:
What we do is take the vertical line of $- 20$ $\text{^"o""C}$ and the horizontal line of $1$ $\text{atm}$ (not explicitly shown here, but it is essentially the bottom of the graph) and find in what phase region they intersect.
Carbon dioxide appears to be in the gaseous state at $- 20$ $\text{^"o""C}$ at all pressures below $20$ $\text{atm}$, so it will be in the gas phase.