Parke's process is used to extract

$FeCr_2O_4$ (chromite) is converted to $Cr$ by following steps:
Chromite $\xrightarrow{I} Na_2CrO_4$ $\xrightarrow{II} Cr_2O_3$ $\xrightarrow{III} Cr$
Reagents in $I, II$ and $III$ steps might be:
$I$ Step $-$ $II$ Step $-$ $III$ Step

Gold is extracted by the formation of a soluble cyanide complex. What is the formula of this cyanide complex?

Blister copper is.......

Matte contains mainly

The metal oxide which cannot be reduced to metal by carbon is