What change occurs in the concentrated ore during the roasting process?

Which kind of impurities are present in the ores? What are these impurities collectively known as?

Which method is used for the purification of semiconductor metals?

Four groups are given linking a metal, its ore, and the chemical formula of the main component of the ore. How many of these are correct?
$(1)$ Iron - Magnetite - $Fe_{3}O_{4}$
$(2)$ Iron - Siderite - $FeS_{2}$
$(3)$ Copper - Copper glance - $Cu_{2}S$
$(4)$ Copper - Dolomite - $Al_{2}O_{3}$

In a blast furnace,what prevents the oxidation of molten iron?

$(i)$ Given below are the steps for the extraction of copper from its ore. Write the reactions involved:
$(a)$ Roasting of copper $(I)$ sulphide
$(b)$ Reduction of copper $(I)$ oxide with copper $(I)$ sulphide
$(c)$ Electrolytic refining
$(ii)$ Draw a neat and well-labelled diagram for the electrolytic refining of copper.