Dry ice is the solid form of which compound?

Dry ice is the solid form of carbon dioxide, or CO₂.

Unlike ordinary water ice, dry ice does not normally melt into a liquid at Earth’s atmospheric pressure. Instead, it sublimates—changing directly from a solid into a gas. At one atmosphere, this occurs at about −78.5 °C, which makes dry ice useful for transporting frozen foods, cooling laboratory samples, and producing theatrical fog when placed in warm water.

Carbon dioxide is a linear molecule containing one carbon atom bonded to two oxygen atoms. Under pressures below about 5.13 atmospheres, it cannot form a stable liquid phase; its solid, liquid, and gas phases meet at the triple point near −56.4 °C and 5.18 bar. The “dry” in dry ice refers to its lack of a liquid residue during ordinary sublimation.

Dry ice must be handled with insulated gloves because it can cause frostbite. In enclosed spaces, released carbon dioxide can accumulate and displace oxygen, so ventilation is essential. Carbon monoxide, water, and nitrogen are different substances and are not dry ice.