The alloy steel used in ball bearings is

Sulphide ores are concentrated by

Roasting is generally used for

Cast iron is purified by heating on the hearth of furnace by a process called

The alloy used in aircraft parts are 

 Limestone is

The material which combines with gangue to form slag is

The corrosion resistance of steel is greatly improved by the addition of 

The hardness of steel increases with the increase in 

  Extraction of the metals from their ores and preparation of alloys is called?