Dry ice is composed of frozen solid what?

Dry ice is composed of frozen solid carbon dioxide. At atmospheric pressure, carbon dioxide exists as a gas, but when it is cooled to a temperature of around -78.5 degrees Celsius, it transitions into a solid form. This solid state is what we refer to as dry ice.

Dry ice is commonly used for refrigeration and creating fog effects because it sublimates directly from a solid to a gas, bypassing the liquid phase. This property makes it particularly useful in applications where moisture needs to be avoided, as it does not leave any liquid residue.

The other options listed do not accurately represent the composition of dry ice. Water, oxygen, and nitrogen do not exist as solid forms under normal atmospheric conditions in the same way that carbon dioxide does in the context of dry ice. Overall, the unique properties of solid carbon dioxide are what define dry ice and distinguish it from other substances.