Chemistry - Coordination Chemistry Question with Solution | TestHub

${\mathrm{H}}_2\mathrm{O}$is weaker ligand than$\text{N}{\text{H}}_3$
So,$({\mathrm{\Delta }}_0{)}_{\mathrm{B}}>({\mathrm{\Delta }}_0{)}_{\mathrm{A}}$
Since, oxidation number of$\mathrm{C}\mathrm{r}$in the complex
${\left[\underset{\text{x0}}{\text{Cr}({\mathrm{H}}_2\mathrm{O}{)}_6}\right]}_{-1}\mathrm{C}{\mathrm{l}}_3$is calculated as,$\underset{=\mathrm{}\mathrm{x}\mathrm{}=\mathrm{}+3}{\mathrm{x}+6\left(0\right)+3(-1)=0}$
So,$\text{C}{\text{r}}^{3+}$has$3{\mathrm{d}}^3$configuration
Similarly, oxidation no. of$\mathrm{C}\mathrm{r}$in
${\left[\underset{\text{x0}}{\text{Cr}(\text{N}{\text{H}}_3{)}_6}\right]}_{-1}$$\text{C}{\text{l}}_3$is calculated as,$\underset{=\mathrm{x}\mathrm{}=\mathrm{}+3}{\mathrm{x}+6\left(0\right)+3(-1)=0}$
So$\text{C}{\text{r}}^{3+}$has$3{\mathrm{d}}^3$configuration
Thus, both A and B are paramagnetic with 3 unpaired electrons.
We know,$\mathrm{\Delta }=\frac{\mathrm{h}\mathrm{c}}{{\mathrm{\lambda }}_{\text{absorbed}}}$

Since$({\mathrm{\Delta }}_0{)}_{\mathrm{B}}>({\mathrm{\Delta }}_0{)}_{\mathrm{A}}$
${\mathrm{\lambda }}_{\mathrm{A}}>{\mathrm{\lambda }}_{\mathrm{B}}$
A is violet coloured so its energy is calculated from yellow colour absorbed.
$({\mathrm{\Delta }}_0{)}_{\mathrm{A}}$or${\mathrm{\Delta }}_{\text{violet}}=\frac{\mathrm{h}\mathrm{c}}{{\mathrm{\lambda }}_{\text{yellow}}}$
Similarly,$({\mathrm{\Delta }}_0{)}_{\mathrm{B}}$or${\mathrm{\Delta }}_{\text{yellow}}=\frac{\mathrm{h}\mathrm{c}}{{\mathrm{\lambda }}_{\text{yellow}}}$
Hence,${\mathrm{\Delta }}_0$values of A and B are calculated from the energies of yellow and violet light respectively.