Which compound is present in limestone that is of significant use?

Limestone primarily consists of calcium carbonate, which is represented by the chemical formula CaCO₃. This compound is of significant importance for various applications. In construction, calcium carbonate is primarily used to produce lime through the process of calcination, where limestone is heated to produce calcium oxide and carbon dioxide. Lime is then used in a range of processes, including making mortar and as a component in cement.

Additionally, calcium carbonate serves other practical purposes, such as being used as a filler in products like paint and plastics, as a dietary calcium supplement in the health sector, and in environmental applications to neutralize acidic soil and water.

The other compounds listed do not play as prominent a role in the context of limestone. Calcium hydroxide, while derived from calcium carbonate, does not naturally occur in limestone. Iron(III) oxide is not a component of limestone, but rather a separate compound involved in producing iron. Sodium bicarbonate, also unrelated to limestone, is used primarily in baking and as a mild antacid. Therefore, calcium carbonate is the key component of limestone that is essential for various industrial and environmental uses.