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JEE Advanced · Chemistry · 23. Coordination Compounds

The correct order of the wavelength maxima of the absorption band in the ultraviolet-visible region for the given complexes is

  1. A \(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} <[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\)\(\left(\mathrm{H}_2 \mathrm{O}\right)]^{3+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5(\mathrm{Cl})\right]^{2+}\)
  2. B \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5(\mathrm{Cl})\right]^{2+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+}\)\(<\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} <\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}\)
  3. C \(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5(\mathrm{Cl})\right]^{2+}\)\(<\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\)
  4. D \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} <\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}\)\(<\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5(\mathrm{Cl})\right]^{2+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} <[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\)\(\left(\mathrm{H}_2 \mathrm{O}\right)]^{3+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5(\mathrm{Cl})\right]^{2+}\)

Step-by-step Solution

Detailed explanation

\(\Delta_{\mathrm{O}} \propto \frac{1}{\lambda}\)
The absorb wave length order is
\(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\)\(<\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5 \mathrm{H}_2 \mathrm{O}\right]^{3+} <\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right]^{2+}\)
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