Correct increasing order for the wavelengths of absorption in the visible region for the complexes of $\mathrm{Co^{3+}}$ is;
- A$[\mathrm{Co(H_2O)_6}]^{3+},\ [Co(en)_3]^{3+},\ [Co(NH_3)_6]^{3+}$
- B$[\mathrm{Co(H_2O)_6}]^{3+},\ [Co(NH_3)_6]^{3+},\ [Co(en)_3]^{3+}$
- C$[\mathrm{Co(NH_3)_6}]^{3+},\ [Co(en)_3]^{3+},\ [Co(H_2O)_6]^{3+}$
- D$[\mathrm{Co(en)_3}]^{3+},\ [Co(NH_3)_6]^{3+},\ [Co(H_2O)_6]^{3+}$
✓ Correct answer: D
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