Explanation:

- Limestone, chalk, and marble are all composed primarily of calcium carbonate. These materials differ mainly in their formation process and physical properties.

- Limestone is a sedimentary rock primarily composed of calcite, a crystalline form of calcium carbonate. It's often formed in clear, warm, shallow marine waters from the accumulation of shell, coral, algal, and other organic debris.

- Chalk is a softer, white form of limestone formed from minute marine organisms like foraminifera.

- Marble is a metamorphic rock formed when limestone is subjected to high pressure or heat, resulting in a denser and more crystalline structure.

- Option 1: Calcium carbonate is the chemical compound found in limestone, chalk, and marble.

- Option 2: Sodium carbonate, also known as soda ash, is used in glassmaking and detergents, but is not found in these rocks.

- Option 3: Potassium carbonate, a chemical used in glass and soap production, isn't relevant to lime, chalk, or marble.

- Option 4: Magnesium carbonate is another mineral found in the earth, but it is not the main component of limestone, chalk, and marble.