A) it melts at \[{{0}^{o}}C\]
B) its BP is more than \[{{199}^{o}}C\]
C) it directly change to vapours lowering the temperature to \[-{{78}^{o}}C\]
D) none of the above
Correct Answer: C
Solution :
Solid \[C{{O}_{2}}\] is known as dry ice. It is obtained when compressed \[C{{O}_{2}}\] gas (at 50-60 atm) is cooled. When solid \[C{{O}_{2}}\] is allowed to evaporate in air at atmospheric pressure, it directly changes in gaseous state without liquifying. Unlike ordinary ice it does not wet the surface on which it melts, therefore, called dry ice. e.g., a temperature of \[-{{78}^{o}}C\] is obtained by using a mixture of dry ice and acetone.
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