The complex showing a spin-only magnetic moment of $2.82$ B.M. is

The complex showing a spin-only magnetic moment of $2.82$ B.M. is
  1. $\mathrm{Ni}(\mathrm{CO})_4$
  2. $\left[\mathrm{NiCl}_4\right]^{2-}$
  3. $\mathrm{Ni}\left(\mathrm{PPh}_3\right)_4$
  4. $\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}$

Solution

$\mathrm{Ni}: 3 d^8 4 s^2 \quad \mathrm{Ni}^{2+}: 3 d^8$ Since, $\mathrm{Cl}$ is a weak field ligand, it doesn't cause pairing of electron.
Number of unpaired electrons, $n=2$ $ \mu=\sqrt{n(n+2)}=\sqrt{2(2+2)} \mathrm{BM}=\sqrt{8} \mathrm{BM}=2.82 \mathrm{BM} $ Coordination compound Conceptual III

Asked in: JEE Advanced 2010 (Paper 2)

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