49. Match the items of Column I with the items of Column II and assign the correct code :

Column I	Column II
(A) Sapphire	(1) Al2O3
(B) Sphalerite	(2) NaCN
(C) Depressant	(3) Co
(D) Corundum	(4) ZnS
	(5) Fe2O3

Code :

A (3) B (4) C (2) D (1)

A (5) B (4) C (3) D (2)

A (2) B (3) C (4) D (5)

A (1) B (2) C (3) D (4)

 $\frac{dE}{dT}$ is the temperature Co-efficient of cell. The cell having less variation of EMF, with respect to temperature have high efficiency.

Below 1350° C, Mg can reduce Al₂O₃ and above 1350°C, Al can reduce MgO (from Ellingham diagram).

Melting and boiling point of Mg are lower than that of Al.

In ores/mineral available earthy and undesired impurities are gangue

Sol. Reactivity towards ${\mathrm{A}\mathrm{g}\mathrm{N}\mathrm{O}}_3$  depend on stability of carbocation formed

Leaching involves the given reaction,

$4Au\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(aq\right)+O_2\left(g\right)\to 4{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$              

Here, O₂ is required for formation of Au (l) cyanide complex but no complex in absence of O₂.

$2{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+Zn\left(s\right)\to {\left[Zn{\left(CN\right)}_4\right]}^{2-}\left(aq\right)+2Au\left(s\right)$                

In above displacement reaction, Zn is oxidized.