Question

Which of the following complex will absorb maximum wavelength of light?

• A. $\left[ Co \left( NH _{3}\right)_{5}\left( H _{2} O \right)\right]^{3+}$
• B. $\left[ CoCl \left( NH _{3}\right)_{5}\right]^{2+}$
• C. $\left[ Co \left( NH _{3}\right)_{6}\right]^{3+}$
• D. $\left[ Co ( CN )_{6}\right]^{3-}$

Answer 1

Answer: (B)

CFSE $\propto$ strength of ligand $\propto1 / \lambda$
$\because$ complex $\left[ CoCl \left( NH _{3}\right)_{5}\right]^{2+}$ has minimum charge among all the complex so has lower CFSE so will absorb maximum wavelength of light.