Solid substance commonly known as ‘dry ice’: A. CaCO3 B. CO C. CO2 D. CaCl2

The correct answer is $\boxed{\text{CO}_2}$.

Dry ice is the solid form of carbon dioxide. It is a white solid that sublimes at -78.5 °C and 1 atm pressure, meaning that it changes directly from a solid to a gas without passing through a liquid state. Dry ice is often used as a refrigerant, as it has a very low temperature and can absorb a large amount of heat. It is also used in theatrical productions and special effects, as it produces a fog-like effect when it sublimates.

The other options are incorrect.

• $\text{CaCO}_3$ is calcium carbonate, which is a white solid that is found in limestone, chalk, and marble.
• $\text{CO}$ is carbon monoxide, which is a colorless, odorless gas that is poisonous.
• $\text{CaCl}_2$ is calcium chloride, which is a white solid that is used as a de-icing agent and a drying agent.