Which of the following complexes have a maximum number of unpaired electrons

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$[Ni (CO)_{4}]$

${[Co {({NH}_{3})}_{4} {({NO}_{2})}_{2}]}^{+}$

${[Ag (CN)_{2}]}^{-}$

${[{CuBr}_{4}]}^{2 -}$

answer is D.

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Detailed Solution

Outer electronic configuration of Ni is $3 d^{8} 4 s^{2} .$ Cyanide is a strong ligand, so in the presence of CN- the 4s electrons shifts to 3d and all electrons gets paired.

In ${[Co {({NH}_{3})}_{4} {({NO}_{2})}_{2}]}^{+}$ , the oxidation state of Co is +3 and having 3d⁶ as outer electronic configuration. In the presence of strong ligands, all electrons gets paired.

In ${[Ag (CN)_{2}]}^{-}$ , Ag has +1 oxidation state and its outer electronic configuration is 3d¹⁰. There is no unpaired electrons.

In ${[{CuBr}_{4}]}^{2 -}$ , Cu has +2 oxidation state and its outer electronic configuration is 3d⁹. There is one unpaired electron.

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