Which statement about carbon dioxide is false?

• A. It can be prepared by the action of acid on limestone
• B. It is used to extinguish fires
• C. It dissolves in water at room temperature
• D. It sublimes rather than melts at 20°C and 1 atmosphere pressure

Answer: (D)

CO2 has a phase behavior with no liquid phase at standard pressure. It exists as a solid only at very low temperatures and as a gas at room temperature and above. So at 20°C and 1 atm, CO2 is a gas, and talking about it subliming versus melting at that condition isn’t a meaningful description of its behavior. The statement is false for that reason. The other points are true: CO2 can be produced by acid reacting with limestone, it is used to extinguish fires by displacing oxygen, and it dissolves in water to form carbonic acid.