Question

Correct increasing order for the wavelengths of absorption
in the visible region the complexes of Co³⁺ is :- [2017]
(a) [Co(H₂O)₆]³⁺, [Co(en)₃]³⁺, [Co(NH₃)₆]³⁺
(b) [Co(H₂O)₆]³⁺, [Co(NH₃)₆]³⁺, [Co(en)₃]³⁺
(c) [Co(NH₃)₆]³⁺, [Co(en)₃]³⁺, [Co(H₂O)₆]³⁺
(d) [Co(en)₃]³⁺, [Co(NH₃)₆]³⁺, [Co(H₂O)₆]³⁺

Answer 1

d)  [Co(en)₃]³⁺, [Co(NH₃)₆]³⁺, [Co(H₂O)₆]³⁺  is the correct order for the wavelength of absorption .

Explanation:

spec t r o chemical series :

I− < Br− < S₂− < SC N − < Cl− < NO₃− < N₃− < F− < OH− < C₂O₄2− < H₂O < N CS− < CH 3 C N < p y < NH₃ < en < bi p y   < p h e n < NO₂− < < C N⁻ < CO

On increasing strength of l i g a n d wavelength of absorbed radiation decreases

order of spectrochemical series=H₂O< NH₃< e{n}

Order of absorbed wavelength==en < NH₃ < H₂O