Silver chloride dissolves in excess of $NH_4OH$. The cation present in this solution is

Arrange the following complexes in the correct increasing order of their electrical conductivity in aqueous solution:
$(I) [Pt(NH_3)_6]Cl_4$
$(II) [Cr(NH_3)_6]Cl_3$
$(III) [Co(NH_3)_4Cl_2]Cl$
$(IV) K_2[PtCl_6]$

For the complex $ML_2$,the stepwise formation constants for the reactions:
$M + L \rightleftharpoons ML$
$ML + L \rightleftharpoons ML_2$
are $4$ and $3$ respectively. Hence,the overall stability constant for the reaction:
$M + 2L \rightleftharpoons ML_2$
is:

When $CuSO_4$ solution in water is treated with concentrated $HCl$,it turns:

$Ag^{+} + NH_3 \rightleftharpoons [Ag(NH_3)]^{+}$; $k_1 = 3.5 \times 10^{-3}$
$[Ag(NH_3)]^{+} + NH_3 \rightleftharpoons [Ag(NH_3)_2]^{+}$; $k_2 = 1.7 \times 10^{-3}$
Then the formation constant of $[Ag(NH_3)_2]^{+}$ is

Identify the correct decreasing order of stability of complexes formed by divalent metal ions with the same ligand.