In the metallurgical extraction of zinc from $ZnO$,the reducing agent used is:

During the smelting of roasted copper ore,silica is added to remove:

Consider the following metallurgical processes:
$(i)$ Heating impure metal with $CO$ and distilling the resulting volatile carbonyl (boiling point $43\,^{\circ}C$) and finally decomposing at $150\,^{\circ}C$ to $200\,^{\circ}C$ to get the pure metal.
$(ii)$ Heating the sulphide ore in air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged sulphide.
$(iii)$ Electrolysing the molten electrolyte containing approximately equal amounts of the metal chloride and $CaCl_2$ to obtain the metal.
The processes used for obtaining sodium,nickel and copper are,respectively,

The addition of silica during the extraction of copper from its sulphide ore:

Match the extraction processes listed in Column $I$ with metals listed in Column $II$:

Column $I$	Column $II$
$A$. Self reduction	$P$. Lead
$B$. Carbon reduction	$Q$. Silver
$C$. Complex formation and displacement by metal	$R$. Copper
$D$. Decomposition of iodide	$S$. Boron

Extraction of metal from the ore cassiterite involves