Question

The correct order of the wavelength of light absorbed by the following complexes is:
A. $[ \text{Co(NH}_3\text{)}_6]^{3+}$
B. $[ \text{Co(CN)}_6]^{3-}$
C. $[ \text{Cu(H}_2\text{O)}_4]^{2+}$
D. $[ \text{Ti(H}_2\text{O)}_6]^{3+}$
Choose the correct answer from the options given below:

• A. B $<$ A $<$ C $<$ D
• B. C $<$ D $<$ A $<$ B
• C. C $<$ A $<$ D $<$ B
• D. B $<$ D $<$ A $<$ C

Hint:

The wavelength of light absorbed by a complex is inversely proportional to the ligand field strength. Strong field ligands (e.g., CN⁻) cause larger d-orbital splitting and absorb light at shorter wavelengths.