The correct order of the complexes [Co(NH_3)_5(H_2 O)]^ 3+ (A), [Co (NH_3)_6]^ 3+ (B), [Co(CN)_6]^ 3- (C) and [CoCl(NH_3)_5]^ 2+ (D) in terms wavelength of light absorbed is :

Correct answer: A. D>A>B>C We know E=h v= hC λ E (1)/(λ) Here all Co in +3 oxidation state. So, as the ligand field strength , CFSE Order of field strength of ligand : CN NH_3 H_2 O Cl^ - CFSE order : C B A D Wavelength order: D A B C

JEE Main 20253 AprilMorning Shift

Exam: JEE Main
Year: 2025
Date: 3 April
Shift: Morning Shift
Subject: Chemistry
Chapter: Coordination Compounds

JEE Main 2025 · 3 April · Morning Shift · Chemistry · Coordination Compounds

The correct order of the complexes [Co(NH_3)_5(H_2 O)]^ 3+ (A), [Co...

The correct order of the complexes

\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+}

(A),
\left[\mathrm{Co}

\left(\mathrm{NH}_3\right)_6\right]^{3+}

(B),
\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}(\mathrm{C})

and \left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right]^{2+}(\mathrm{D})

in terms wavelength of light absorbed is :

Options

AD>A>B>C
BC>B>D>A
CD>C>B>A
DC>B>A>D

Correct answer

A. D>A>B>C

Step-by-step solution

We know

\mathrm{E}=\mathrm{h} v=\frac{\mathrm{hC}}{\lambda}

\mathrm{E} \propto \frac{1}{\lambda}

Here all Co in +3 oxidation state.
So, as the ligand field strength

\uparrow, \operatorname{CFSE} \uparrow

Order of field strength of ligand :

\mathrm{CN} \gt \mathrm{NH}_3 \gt \mathrm{H}_2 \mathrm{O} \gt \mathrm{Cl}^{-}

CFSE order :

\mathrm{C} \gt \mathrm{B} \gt \mathrm{A} \gt \mathrm{D}

Wavelength order:

\mathrm{D} \gt \mathrm{A} \gt \mathrm{B} \gt \mathrm{C}

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