Answer the following questions based on the p-T phase diagram of carbon dioxide as shown in the figure .
(i) At what temperature and pressure can the solid , liquid and vapour phases of `C0_(2)` co-exist in equilibrium?
(ii) What is the effect of decrease of pressure on the fusion and boiling point of `C0_(2)` ?
(iii) What are the critical temperature and pressure for `C0_(2)` ? what is their significance ?
(iv) Is `C0_(2)` solid , liquid, or gas at (a) `-70^(@)C `under 1 atm (b) `-60^(@)C` under 10 atm (c) `15^(@)C` under 56 atm ?

Explanation

The critical temperature and pressure of `CO_(2) " are " 31.1 ^(@) C " and " 73.0 ` atm, respectively. Above this temperature, `CO_(2)` will not liquefy even if compressed to high pressures.