$$\eqalign{ & {\text{In Hall - Heroult process,}} \cr & {\text{At cathode :}}\,Al_{\left( {{\text{melt}}} \right)}^{3 + } + 3{e^ - } \to A{l_{\left( l \right)}} \cr & {\text{At anode :}}\,{C_{\left( s \right)}} + O_{\left( {{\text{melt}}} \right)}^{2 - } \to C{O_{\left( g \right)}} + 2{e^ - } \cr & {C_{\left( s \right)}} + 2O_{\left( {{\text{melt}}} \right)}^{2 - } \to C{O_{2\left( g \right)}} + 4{e^ - } \cr} $$

Copper matte consists of $$C{u_2}S$$  and $$FeS.$$

Since silica is acidic impurity the flux must be basic.
$$CaO + Si{O_2} \to CaSi{O_3}$$

In the electrolytic refining of copper the more electropositive impurities like $$Fe,Zn,Ni,Co,$$   etc. dissolve in the solution and less electropositive impurities such as $$Ag,Au$$  and $$Pt$$  collect below the anode in the form of anodic mud.

For each $$kg$$  of $$Al$$  produced, about $$0.5\,kg$$  of carbon anode is burnt away.

Since reduction potential of $$Al$$  is more than that of $$Mg$$  and less than other given metals. So it cannot reduce $$Mg$$  from its oxide.

Gypsum is an ore of calcium and not of magnesium. The structural formula of gypsum is $$CaS{O_4} \cdot 2{H_2}O.$$

No explanation is given for this question. Let's discuss the answer together.

No explanation is given for this question. Let's discuss the answer together.

Extraction of gold and silver involves leaching with $$C{N^ - }$$   $$ion.$$  Silver is later recovered by distillation of $$Zn.$$
In the metallurgy of silver or gold, the respective metal is leached with a dilute solution of $$NaCN$$  or $$KCN$$  in the presence of air to obtain the metal in solution as complex. From the complex, metal is obtained later by replacement.
In general,
$$4M\left( s \right) + 8C{N^ - }\left( {aq} \right) + $$     $$2{H_2}O\left( {aq} \right) + {O_2}\left( g \right) \to $$     $$4{\left[ {M{{\left( {CN} \right)}_2}} \right]^ - }\left( {aq} \right) + 4O{H^ - }\left( {aq} \right)$$
$$2{\left[ {M{{\left( {CN} \right)}_2}} \right]^ - }\left( {aq} \right) + Zn\left( s \right)$$     $$ \to {\left[ {Zn{{\left( {CN} \right)}_4}} \right]^{2 - }}\left( {aq} \right) + 2M\left( s \right)$$
$$M = Ag\,\,{\text{or}}\,Au$$
This method is known as Mac-Arthur Forest cyanide process.