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Chemistry · Coordination Compounds

JEE Main 2026 — 24 January, Evening Shift — Question 54

The wavelength of light absorbed for the following complexes are in the order. [Co(NH3)6 (I) ]3+;[Co(H2O)6 (II) ]3+;[Co(CN)6 (III) ]3−;\left.\left.\left[\underset{\text { (I) }}{\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}}\right]^{3+} ; \underset{\text { (II) }}{\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right.}\right]^{3+} ; \underset{\text { (III) }}{\left[\mathrm{Co}(\mathrm{CN})_{6}\right.}\right]^{3-} ; Co(NH3)5(H2O)]3+(IV);[CoF6]3−(V)\underset{(\mathrm{IV})}{\left.\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}} ; \underset{(\mathrm{V})}{\left[\mathrm{CoF}_{6}\right]^{3-}}

  1. Option A:

    III << I << II << IV << V

  2. Option B:

    III << I << IV << V << II

  3. Option C:

    III << IV << I << II << V

  4. Option D:

    III << I << IV << II << V

    Correct

Answer: D

Step-by-step solution

Wavelength of light absorbed increases as C.F.S.E of complex decreases. [Co(CN)6]3−\left[\mathrm{Co}(\mathrm{CN})_{6}\right]^{3-} has maximum CFSE [CoF6]3−\left[\mathrm{CoF}_{6}\right]^{3-} has least CFSE Ligand field strength ↑ ; C.F.S.E ↑ Correct wavelength order. V >> II >> IV >> I >> III

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Paper
24 January, Evening Shift
Subject
Chemistry
Chapter
Coordination Compounds
Topic
Properties and importance of Coordination Complexes

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