question_answer

Which one of the following complex ions has the highest magnetic moment?

A)  \[{{[Cr{{(N{{H}_{3}})}_{6}}]}^{3+}}\]      

B)  \[{{[Fe(C{{N}_{6}})]}^{3-}}\]

C)  \[{{[Fe(C{{N}_{6}})]}^{4-}}\]     

D)  \[{{[Zn{{(N{{H}_{3}})}_{6}}]}^{2+}}\]

Correct Answer: A

Solution :

                Higher the number of unpaired electrons, higher is the magnetic moment. In\[{{[Fe{{(CN)}_{6}}]}^{3-}},\]one unpaired electron is present and in\[{{[Fe{{(CN)}_{6}}]}^{4-}}\]and\[{{[Zn{{(N{{H}_{3}})}_{6}}]}^{2+}}\] both unpaired electrons are absent. Hence, \[{{[Cr{{(N{{H}_{3}})}_{6}}]}^{3+}}\]has the highest magnetic moment among the given complex ions. \[[\mu =\sqrt{3(3+2)}=3.878\,BM]\]. (\[C{{N}^{-}}\]is a strong field ligand, thus causes pairing.)