$CuSO_4$ decolourises on addition of $KCN$,the product is

$X$ is the number of electrons in $t_{2g}$ orbitals of the most stable complex ion among $[Fe(NH_3)_6]^{3+}$,$[Fe(Cl)_6]^{3-}$,$[Fe(C_2O_4)_3]^{3-}$ and $[Fe(H_2O)_6]^{3+}$. The nature of the oxide of vanadium of the type $V_2O_X$ is:

$PtCl_4 \cdot 6H_2O$ can exist as a hydrated complex. Its $1 \ m$ aqueous solution has a depression in freezing point of $3.72 \ ^\circ C$. Assuming $100\%$ ionization and $K_f \ (H_2O) = 1.86 \ ^\circ C \ kg \ mol^{-1}$,the correct formula for the complex is:

The green coloured complex ion of nickel in its aqueous solution is

The most stable ion 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: