Statement A

Ethane−$1,2$−diamine is a chelating agent as it contains two coordinating sites that are two nitrogen atoms which donate their lone pairs of electrons and can form a $5$-membered ring with the metal ion.

Statement B

Based on Hall-Heroults process-

The Hall-Heroult process is widely used in the extraction of aluminium. In Hall-Heroults process, pure ${\mathrm{Al}}_2{\mathrm{O}}_3$is mixed with ${\mathrm{CaF}}_2 \mathrm{or} {\mathrm{Na}}_3{\mathrm{AlF}}_6$. This results in lowering the melting point of the mixture and increases its ability to conduct electricity.  A steel vessel with a lining of carbon and graphite rods is used.

Statement C

Cyanide ion is used as ligand for leaching of silver.

The cyanide process, which is also known as the Macarthur-forest process, is widely used in extracting gold or silver from the ores by dissolving them in a dilute solution of potassium cyanide or sodium cyanide.

Statement D 

$\left[\mathrm{Rh}{\left({\mathrm{PPh}}_3\right)}_3\mathrm{Cl}\right]$ Wilkinson's catalyst

Statement E

${\mathrm{Ca}}^{++}$ ion forms more stable complex with EDTA

Hence option C is the answer.