The correct answer is option 2: Calcium carbonate.

Chalk and marble are indeed different forms of calcium carbonate. Calcium carbonate is a chemical compound composed of calcium, carbon, and oxygen. It is commonly found in nature in various forms, including chalk and marble.

Chalk is a soft, white, porous sedimentary rock primarily composed of calcium carbonate. It is commonly used in classrooms for writing on chalkboards.

Marble, on the other hand, is a metamorphic rock that is formed from limestone through a process of heat and pressure. It is characterized by its smooth and shiny surface and is widely used as a building material and in sculpture.

Calcium hydrogen carbonate (option 1) is not correct because it is a bicarbonate compound and does not form the basis of chalk or marble.

Calcium acetate (option 3) is also incorrect. It is a different compound that is used in various medical and industrial applications.

Sodium carbonate (option 4) is not the correct answer either. While it is a carbonate compound, it is not related to the formation of chalk or marble.

Therefore, the correct answer is option 2: Calcium carbonate.