Chemistry - Coordination Chemistry Question with Solution | TestHub

$${\mathrm{Ni}}^{2+}+4{\mathrm{CN}}^{-}⟶{\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{2-}\text{. Here }{\mathrm{Ni}}^{2+}\text{ has }{d}^8\text{ configuration with }{\mathrm{CN}}^{-}\text{as strong ligand. }$$
$d^8$-configuration in strong ligand field gives $ds{p}^2$-hybridisation, hence square planar geometry. $${\mathrm{Ni}}^{2+}+4{\mathrm{Cl}}^{-}⟶{\left[{\mathrm{NiCl}}_4\right]}^{2-}$$ Here ${\mathrm{Ni}}^{2+}$ had $d^8$-configuration with ${\mathrm{Cl}}^{-}$as weak ligand.
$d^8$-configuration in weak ligand field gives $s{p}^3$ hydridisation, hence tetrahedral geometry. ${\mathrm{Ni}}^{2+}$ with ${\mathrm{H}}_2\mathrm{O}$ forms ${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$ complex and ${\mathrm{H}}_2\mathrm{O}$ is a weak ligand.
$$\text{ Therefore, }\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}^{2+}\text{ has octahedral geometry. }$$