Question

The correct order of the wavelength of light absorbed by the following complexes is:

1. [Co(NH₃)₆]³⁺
2. [Co(CN)₆]³⁻
3. [Cu(H₂O)₄]²⁺
4. [Ti(H₂O)₆]³⁺

Choose the correct answer from the options given below:

Options

• B < D < A < C

• B  <  A < D < C

• C < D < A < B

• C < A < D < B

Answer 1

B  <  A < D < C

Explanation:

The wavelength of light absorbed (λ) is inversely proportional to the Crystal Field Splitting Energy (Δ).

E = Δ = `(hc)/λ`

The value of Δ depends on the Spectrochemical Series and the oxidation state of the metal:

Ligand Strength: CN⁻ > NH₃ > H₂O)

Oxidation State of Metal: A higher charge on the metal increases Δ (M³⁺ > M²⁺).

A stronger field (higher Δ) results in a shorter wavelength of light being absorbed.

[Co(CN)₆]³⁻ > [Co(NH₃)₆]³⁺ > [Ti(H₂O)₆]³⁺ > [Cu(H₂O)₄]²⁺