Calcination is used for removal of volatile impurities and decompose carbonates.

Purified $$A{l_2}{O_3}$$  is mixed with $$N{a_3}Al{F_6}$$   and $$Ca{F_2}$$  to improve conductivity of $$A{l_2}{O_3}$$  and to lower the melting point.
\[A{{l}_{2}}{{O}_{3}}\xrightarrow{\text{electrolysis}}2A{{l}^{3+}}+3{{O}^{2-}}\]
$$\eqalign{ & {\text{At cathode}}:A{l^{3 + }} + 3{e^ - } \to Al \cr & {\text{At anode}}:\,\,\,C + {O^{2 - }} \to CO + 2{e^ - } \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C + 2{O^{2 - }} \to C{O_2} + 4{e^ - } \cr} $$

Cassiterite contains the magnetic impurities of $$FeS{O_4}$$  and concentrated by electromagnetic separation.

Reduction with carbon is known as smelting.

NOTE : During the extraction of copper, iron is present in the ore as impurity $$\left( {FeS} \right)$$.
The ore together with a little coke and silica is smelted; $$FeS$$  present as impurity in the ore is oxidized to iron oxide, which then reacts with silica to form fusible ferrous silicate which is removed as slag.
$$2FeS + 3{O_2} \to 2FeO + 2S{O_2} \uparrow ;$$
$$FeO + Si{O_2} \to \mathop {FeSi{O_3}}\limits_{\left( {Slag} \right)} $$

$$C\left( s \right) + \frac{1}{2}{O_2}\left( g \right) \to CO\left( g \right);\Delta S$$       increases. Hence, as the temperature increases, $$T\Delta S$$  increases and hence $$\Delta G\left( {\Delta H - T\Delta S} \right)$$    decreases. In other words, the slope of the curve for formation of $$CO$$  decreases. However, for all other oxides, it increases.

$$NaCN + ZnS \to \mathop {N{a_2}\left[ {Zn{{\left( {CN} \right)}_4}} \right]}\limits_{{\text{Soluble complex}}} $$
A layer of this zinc complex is formed on the surface of $$ZnS$$  and due to this $$ZnS$$  is prevented from the froth formation while $$PbS$$  form froth. ( i.e., $$NaCN$$  is added as depressant for $$ZnS$$  )

\[\begin{align} & Zr\text{ and }Ti\text{ are purified by van Arkel method}\text{.} \\ & \text{Zr}\left( s \right)+2{{I}_{2}}\left( g \right)\xrightarrow{870K}Zr{{I}_{4}}\left( g \right) \\ & Zr{{I}_{4}}\left( g \right)\xrightarrow[\text{Tugsten filament}]{2075K}Zr\left( s \right)+2{{I}_{2}}\left( g \right) \\ & Ti\left( s \right)+2{{I}_{2}}\left( s \right)\xrightarrow{523K}Ti{{I}_{4}}\left( g \right) \\ & Ti{{I}_{4}}\xrightarrow{1700K}\underset{\text{Pure titanium}}{\mathop{Ti\left( s \right)}}\,+2{{I}_{2}}\left( g \right) \\ \end{align}\]

$$MgO$$  acts as a basic flux to remove impurities of $$Si,P$$  and $$S$$  through slag formation.
\[\underset{\begin{smallmatrix} \text{Basic} \\ \text{flux} \end{smallmatrix}}{\mathop{MgO}}\,+\underset{\begin{smallmatrix} \text{Acidic} \\ \text{impurities} \end{smallmatrix}}{\mathop{Si{{O}_{2}}}}\,\to \underset{\text{Slag}}{\mathop{MgSi{{O}_{3}}}}\,\]
$$\eqalign{ & 3MgO + {P_2}{O_5} \to M{g_3}{\left( {P{O_4}} \right)_2} \cr & MgO + S{O_2} \to MgS{O_3} \cr} $$

$$S{O_2}$$  gas is obtained when any sulphide ore is toasted.
$$2{M_2}S + 3{O_2}\mathop \to \limits^\vartriangle 2{M_2}O + 2S{O_2}$$
This gas exhibits all the characteristics that are given in the question.