Isolation of Elements

Among the following ores Bauxite, Siderite, Cuprite, Calamine, Haematite, Kaolinite, Malachite, Magnetite, Sphalerite, Limonite, Cryolite, the number of principal ores if iron is _____________.

(a) Baryte, (b) Galena, (c) Zinc blende and (d) Copper pyrites. How many of these minerals are sulphide based?

In the electrolytic refining of blister copper, the total number of main impurities, from the following, removed as anode mud is ______________

Pb, Sb, Se, Te, Ru, Ag, Au and Pt

Galena (an ore) is partially oxidized by passing air through it at high temperature. After some time, the passage of air is stopped, but the heating is continued in a closed furnace such that the contents undergo self-reduction. The weight (in kg) of $Pb$ produced per kg of ${O_2}$ consumed is ___________.

(Atomic weights in $g\,mo{l^{ - 1}}:O = 16,S = 32,Pb = 207$)

Give briefly the isolation of magnesium from sea water by the Dow process. Give equations for the steps involved.

Give reasons of the following:
Why is sodium chloride added during electrolysis of fused anhydrous magnesium chloride?