Explanation

(b)
$Ni^{2 +} + 4CN^{-} \rightarrow \left\lbrack Ni(CN)_{4} \right\rbrack^{2 -}$
Here $Ni^{2 +}$ has $d^{8}$-configuration with $CN^{-}$ as strong ligand.
[image:9_image205.emf]
$d^{8}$-configuration in strong ligand field gives $dsp^{2}$ hybridisation, hence square planar geometry.
$Ni^{2 +} + 4Cl^{-} \rightarrow \left\lbrack NiCl_{4} \right\rbrack^{2 -}$
Here $Ni^{2 +}$ has $d^{8}$-configuration with $CN^{-}$ as weak ligand.
[image:9_image206.emf]
$d^{8}$-configuration in weak ligand field gives $sp^{3}$hybridisation, hence tetrahedral geometry.
$Ni^{2 +}$ with $H_{2}O$ forms $\left\lbrack Ni\left( H_{2}O \right)_{6} \right\rbrack^{2 +}\$complex and $H_{2}O$ is a weak ligand.
3d
[table] ⥮ | ⥮ | ⥮ | $\upharpoonleft$ | $\upharpoonleft$ [/table]
[image:9_image207.emf]
Therefore, $\left\lbrack Ni\left( H_{2}O \right)_{6} \right\rbrack^{2 +}$has octahedral geometry.