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 used to line furnaces and other high-temperature equipment to protect them from the heat and corrosion. Magnesite is also used in the manufacture of ceramics, glass, and other products.
Limestone is a calcium carbonate mineral that is used in a variety of applications, including construction, agriculture, and the manufacture of cement. 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. Limestone, feldspar, and bauxite are not refractory materials and are not used in the steel industry.