Question

Electric furnaces are lined with magnesia because
A. It is not affected by acids
B. It gives oxygen on heating
C. It melts at very high temperature
D. It has no effect of electricity

Answer 1

Hint: The compound which melts at very high does not react with the metal of the furnace. Magnesia has a high melting point and melts at the temperature of the electric furnace.

Complete Step by Step Answer:
Furnace works at a very high temperature. Thus the metal oxide should have a very high melting point to work at that temperature otherwise the metal oxide will burn.
In magnesium oxide or magnesia, magnesium is an electropositive and oxygen is an electronegative element. So, they form a very strong bond between them and possess a very high melting point. Thus it is used in the furnace.
Thus the correct option is C.

Additional information: Magnesia is actually magnesium oxide. It has the chemical formula of $MgO$ . It has an alkaline earth metal that is magnesium and group sixteen element oxygen.
Magnesium oxide reacts with water to form magnesium hydroxide. It is a basic hydroxide.

Note: Another metal oxide used in furnace is Calcium oxide. It has high melting point and widely used in the furnace. It is an oxide of calcium, an alkaline earth metal.