Q.Describe the importance of the following :

(i) Limestone (CaCO$_3$)

Limestone is one of the most important raw materials in the chemical and construction industries: it is used to manufacture quicklime (CaO) and cement, is used as a building and monument stone, acts as a flux in the blast-furnace extraction of iron (removing silicate impurities as slag), and provides both the CaO and CO$_2$ needed in the Solvay process for manufacturing sodium carbonate.

(ii) Cement

Cement, made mainly from limestone and clay, is one of the most important building materials in the modern world. When mixed with water, sand and gravel it forms concrete and mortar, used in the construction of buildings, bridges, dams and roads — cement is indispensable to virtually all large-scale civil engineering.

(iii) Plaster of Paris (CaSO$_4 \cdot \tfrac{1}{2}H_2O$) …

Give each compound's role in industry/medicine explicitly: limestone as a versatile raw material (cement, quicklime, flux, Solvay feedstock), cement as the backbone building material for concrete, and plaster …

• Describing limestone and cement as though they were the same substance — limestone is the raw material, cement is a manufactured product derived (in part) from it.
• Omitting plaster of Paris's defining chemical property (that it re-hydrates and hardens/sets), which is the reason it's used for orthopaedic casts. …