Which of the following is an ore of calcium?

Ore of calcium is dolomite. Its formula is CaMg(CO3)2. 

Calcium as an element is found only in living creatures, but its ores are abundant and the major mined ores are calcite , gypsum, and anhydrite

These ores are mined to extract calcium or its compounds for use in different industries. Examples of calcium ores include:

1. Dolomite (CaMg(CO₃)₂):
   • A significant ore of calcium that also contains magnesium.
   • It is widely used in the production of cement, as a soil conditioner in agriculture, and as a source of magnesium oxide.
2. Calcite (CaCO₃):
   • A common mineral that forms limestone and marble.
   • It is used in the manufacture of cement, lime, and as a filler in various products like paints and plastics.
3. Gypsum (CaSO₄·2H₂O):
   • A hydrated calcium sulfate mineral.
   • It is mainly used to make plaster of Paris, drywall, and as a soil amendment in agriculture.
4. Anhydrite (CaSO₄):
   • An anhydrous form of calcium sulfate.
   • It is utilized in cement production and as a drying agent in industrial applications.

These ores are abundant in the Earth's crust and serve as crucial raw materials in construction, agriculture, and other industries. The specific ore chosen for extraction depends on its availability and the required application.