Carbon dioxide $CO2$ is a colorless and odorless gas that is produced by the combustion of fossil fuels and the respiration of living organisms. It is a key component of the Earth's atmosphere and plays a crucial role in regulating the planet's temperature.

Potassium carbonate $K2CO3$ is a white, granular substance that is commonly used in the production of glass, soaps, and detergents. It is also used as a buffering agent in certain chemical processes.

Calcium carbonate $CaCO3$ is a white, powdery substance that is found in limestone, chalk, and marble. It is used in a variety of applications, including as a dietary supplement, a building material, and a fertilizer.

Calcium oxide $CaO$, also known as quicklime, is a white, crystalline substance that is produced by heating calcium carbonate at high temperatures. It is used in a variety of industrial processes, including the production of cement, steel, and paper.

These compounds are all related to the element carbon and are important in various industries and chemical processes.