Which equilibrium can be described as an acid-base reaction using the Lewis acid-base definition but not using the Bronsted-Lowry definition?

$CuSO_4$ solution reacts with excess $KCN$ to give

In the following reaction sequence in aqueous solution,the species $X, Y$ and $Z$,respectively,are

The $\pi-$acid ligand which uses its $d-$orbital during synergic bonding in its complex compound is:

Choose the correct statements from the following:
$A$. Ethane$-1, 2-$diamine is a chelating ligand.
$B$. Metallic aluminium is produced by electrolysis of aluminium oxide in the presence of cryolite.
$C$. Cyanide ion is used as a ligand for the leaching of silver.
$D$. Phosphine acts as a ligand in Wilkinson's catalyst.
$E$. The stability constants of $Ca^{2+}$ and $Mg^{2+}$ are similar with $EDTA$ complexes.
Choose the correct answer from the options given below:

Out of the following complex compounds,which of the compound will have the minimum conductance in solution?