__________ of carbon blocks in the hearth of blast furnace helps in avoiding skull formation, when it becomes cold.

Highest melting (m.p = 3070°C) oxide refractory is

A. Alumina

B. Thoria

C. Zirconia

D. Magnesia

Fusion point of an acidic refractory material is

A. Increased by the addition of basic oxides

B. Reduced by the addition of basic oxides

C. Not affected by the addition of basic oxides

D. None of the above

Which of the following is not a high alumina refractory material?

A. Kyanite

B. Sillimanite

C. Diaspore

D. Periclase

Magnesite refractories are generally not used in the

A. Electric furnace walls

B. Steel melting furnace

C. Open hearth furnace

D. Burning zone of cement kilns