The correct answer is a) magnesite. Magnesite is a magnesium carbonate mineral that is used as a refractory material in the steel industry. It is also used in the manufacture of ceramics, glass, and other products.
Limestone is a sedimentary rock composed mainly of calcium carbonate. It is used in the manufacture of cement, lime, and other products.
Feldspar is a group of minerals that are used in the manufacture of glass, ceramics, and other products.
Bauxite is an aluminum ore that is used in the manufacture of aluminum.
Magnesite is the correct answer because it is a refractory material that is used in the steel industry. It is a hard, white mineral that is resistant to heat and corrosion. It is used in the lining of furnaces and other high-temperature equipment.