What is the incorrect statement regarding two given complexes $\left[\text{Cr}\left({\text{H}}_{\text{2}}{\text{O}}_{\text{6}}\right){\text{Cl}}_{\text{3}}\right]\left(\text{A}\right)$ and $\left[\text{Cr}{\left({\text{NH}}_{\text{3}}\right)}_6\right]{\text{Cl}}_{\text{3}}\left(\text{B}\right),$  which are violet and yellow coloured respectively?

• A

  Both are paramagnetic with three unpaired electrons
• B

  ${\mathrm{\Delta }}_0$ value of $\left(\mathrm{A}\right)$ is less than that of $\left(\mathrm{B}\right)$
• Correct answer
  C

  ${\mathrm{\Delta }}_0$ values of $\left(\mathrm{A}\right)$ and $\left(\mathrm{B}\right)$ are calculated from the energies violet and yellow light, respectively.
• D

  Both absorb energies corresponding to their complementary colors.

Solution

${\left({\text{Δ}}_0\right)}_{\text{A}}<{\left({\text{Δ}}_0\right)}_{\text{B}}$, both complexes have $\mathrm{CN}=6,$ $\mathrm{B}$ has strong field ligand and $\mathrm{A}$ has weak field ligand

so ${\left({\text{Δ}}_0\right)}_{\text{A}}<{\left({\text{Δ}}_0\right)}_{\text{B}}$

In both complexes, $\mathrm{Cr}$ has $3$ unpaired electrons and hence, will be paramagnetic $\left[\mathrm{Cr}\left({\mathrm{H}}_2\mathrm{O}\right)\right]{\mathrm{Cl}}_3$

$\left[{\mathrm{Cr}}^{+3}=1{\mathrm{S}}^{2}2{\mathrm{S}}^{2}2{\mathrm{p}}^{6}3{\mathrm{S}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^3\right]$ in strong field ligand or weak field ligand is ${\mathrm{t}}_{2\mathrm{g}}^{111},{\mathrm{eg}}^{\mathrm{o}}$



${\mathrm{\Delta }}_0$ order will be compared by spectrochemical series not by energies of violet and yellow light. Hence incorrect

Hence, the correct answer is option: 'C'.