I) The chief ore used to extract lead metal is Galena (PbS).

a)

i) The chief ore used to extract lead metal is Galena ($\text{PbS}$).

ii) At the purification stage, froth flotation is used to concentrate the ore by separating lead sulfide from gangue (impurities).

iii) The equation for the reaction that takes place when the ore is roasted in air is:

$$2\text{PbS(s)} + 3\text{O}_2\text{(g)} \to 2\text{PbO(s)} + 2\text{SO}_2\text{(g)}$$

iv)
T: Lead(II) oxide ($\text{PbO}$)
K: Limestone ($\text{CaCO}_3$)
C: Carbon dioxide ($\text{CO}_2$)
B: Refining (or Purification)
E: Sulfur dioxide ($\text{SO}_2$)

v) Iron is used in the blast furnace to remove sulfur impurities from lead sulfide:

$$\text{Fe(s)} + \text{PbS(s)} \to \text{FeS(l)} + \text{Pb(l)}$$

vi) Tetraethyl lead is being phased out because lead compounds are toxic and cause environmental pollution and health problems, particularly affecting the nervous system. It also poisons catalytic converters in vehicles.

b)

i) The method used to purify (concentrate) the copper ore is Froth flotation.

ii) In the reaction $\text{Cu}_2\text{S} + 2\text{Cu}_2\text{O} \to \text{Cu} + \text{SO}_2$, the reducing agent (L) is Copper(I) sulfide ($\text{Cu}_2\text{S}$).