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The species that has a spin-only magnetic moment of 5.9 BM, is – (Td = tetrahedral) (1) [Ni(CN)4]2− (square planar) (2) Ni(CO)4 (Td) (3) [MnBr4]2− (Td) (4) [NiCl4]2− (Td)

1. (1) [Ni(CN)4]2− (square planar)
2. (2) Ni(CO)4 (Td)
3. (3) [MnBr4]2− (Td)
4. (4) [NiCl4]2− (Td)

Correct answer: (2) Ni(CO)4 (Td)

Solution

Ni(CO)4 has a tetrahedral geometry and contains nickel in the zero oxidation state, allowing it to have 10 d-electrons. Since all these electrons are paired, it results in a spin-only magnetic moment of 5.9 BM, indicating the presence of unpaired electrons.

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