The correct answer is A. Alumina.
Alumina is a chemical compound with the formula Al2O3. It is the most abundant metal oxide in the Earth’s crust, and it is the main component of bauxite, the ore from which aluminum is extracted. Alumina is also a major component of clay, and it is the ingredient in brick earth that enables the brick to retain its shape.
Silica is a chemical compound with the formula SiO2. It is the second most abundant mineral in the Earth’s crust, and it is the main component of sand. Silica is also a major component of clay, but it does not play a role in the brick’s ability to retain its shape.
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal that is found in the Earth’s crust in its elemental form and in various minerals. Iron is the fourth most abundant element in the Earth’s crust, and it is the most abundant metal. Iron is a major component of steel, and it is also used in many other applications, such as construction, transportation, and manufacturing. Iron does not play a role in the brick’s ability to retain its shape.
Magnesia is a chemical element with the symbol Mg and atomic number 12. It is a silvery-white metal that is found in the Earth’s crust in its elemental form and in various minerals. Magnesia is the eighth most abundant element in the Earth’s crust, and it is the third most abundant metal. Magnesia is used in many applications, such as ceramics, pharmaceuticals, and construction. Magnesia does not play a role in the brick’s ability to retain its shape.