In which of the following isolations is no reducing agent required?

Formation of metallic copper from the sulphide ore in the commercial thermo-metallurgical process essentially involves which one of the following reactions as the major reaction?

During the extraction of sodium metal by electrolysis,a mixture of $40\% \ NaCl$ and $60\% \ CaCl_2$ is used because...

$A$ metal has a high concentration in the Earth's crust and its oxides cannot be reduced by carbon. The most suitable method for the extraction of such metal is:

$I$. $FeCr_2O_4 + NaOH + \text{air} \rightarrow Na_2CrO_4 + Fe_2O_3$
$II$. $Na_2CrO_4 + H_2SO_4 \rightarrow Na_2Cr_2O_7$
$Na_2CrO_4$ and $Fe_2O_3$ are separated by:

Identify the correct statements for the following reaction sequence:
$Ag + NaCN (0.5\%) + H_2O + O_2 \to \text{Soluble complex} \xrightarrow{Zn} B (\text{complex}) + Ag$