An octahedral complex $\text{'}\mathrm{X}\text{'}$ with magnetic moment $3.87 \mathrm{BM}$ may have:

(a) ${\mathrm{d}}^3$ configuration with weak field ligand.

(b) ${\mathrm{d}}^3$ configuration with strong field ligand.

(c) ${\mathrm{d}}^6$ configuration with strong field ligand.

(d) ${\mathrm{d}}^7$ configuration with weak field ligand.

The moles of $\mathrm{AgCl}$ precipitated per mole of the following complex, respectively, are $0, 2, 1$ and $2$.

$\left(\mathrm{i}\right)$ ${\mathrm{PtCl}}_2·2{\mathrm{NH}}_3$

$\left(\mathrm{ii}\right)$ ${\mathrm{NiCl}}_2·6{\mathrm{H}}_2\mathrm{O}$

$\left(\mathrm{iii}\right)$ ${\mathrm{CoCl}}_3·4{\mathrm{NH}}_3$

$\left(\mathrm{iv}\right)$ ${\mathrm{PdCl}}_2·4{\mathrm{NH}}_3$

Based on the above information, the secondary valency of:

$\left(\mathrm{a}\right)$ Platinum is $4$       $\left(\mathrm{b}\right)$ Cobalt is $6$

$\left(\mathrm{c}\right)$ Nickel is $2$            $\left(\mathrm{d}\right)$ Palladium is $4$

A metal complex having composition $\mathrm{Cr}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{IBr}}_2$, was isolated in two forms $\mathrm{X}$ and $\mathrm{Y}$($\mathrm{Br}$ is bromine and $\mathrm{I}$ is iodine).

(a) $\mathrm{X}$ reacts with ${\mathrm{AgNO}}_3$ and gives a pale yellow precipitate which is insoluble in ${\mathrm{NH}}_4\mathrm{OH}$.

(b) $\mathrm{Y}$ reacts with ${\mathrm{AgNO}}_3$ and gives a yellow precipitate which is insoluble in ${\mathrm{NH}}_4\mathrm{OH}$.