(i) Cassiterite contains iron and manganese tungstate, called as Wolframite.

They have magnetic properties.

(ii) Purified ore that contains 70% $\text{Sn}{\text{O}}_2$ is called black tin.

$\text{Sn}{\text{O}}_2+2\mathrm{C}\to \text{Sn}+2\text{CO}$ (carbon reduction)

(iii) Roasting is done at moderate temperature in presence of air in reverberatory furnace. Then air supply is stopped and temperature is increased to melt the mass when self

reduction takes place.

(iv) At 500 to 800K (lower temperature range in the upper part of blast furnace)

$3\text{F}{\text{e}}_2{\mathrm{O}}_3+\mathrm{C}\mathrm{O}\to 2\text{F}{\text{e}}_3{\mathrm{O}}_4+\text{C}{\text{O}}_2$

$\text{F}{\text{e}}_3{\mathrm{O}}_4+\mathrm{C}\mathrm{O}\to 3\text{Fe}+4\text{C}{\text{O}}_2$

$\text{F}{\text{e}}_2{\mathrm{O}}_3+\mathrm{C}\mathrm{O}\to 2\text{FeO}+\text{C}{\text{O}}_2$

At 900 to $1500\mathrm{K}$ (higher temperature range in the lower part of blast furnace:

$\mathrm{C}+\text{C}{\text{O}}_2\to 2\text{CO}$ , $\text{FeO}+\mathrm{C}\mathrm{O}\to \mathrm{F}\mathrm{e}+\text{C}{\text{O}}_2$