An atom in a molecule has electrons in $1\mathrm{s},2\mathrm{s}$,$2\mathrm{p},3\mathrm{s},3\mathrm{p},3\mathrm{d}$ and $4\mathrm{s}$ orbitals. This atom can undergo hybridizations of type

An atom in a molecule has electrons in $1\mathrm{s},2\mathrm{s},2\mathrm{p},3\mathrm{s},3\mathrm{p},3\mathrm{d}$ and $4\mathrm{s}$ orbitals Thus the outermost most valence shell composed of $3 \mathrm{d}$ orbitals. $3 \mathrm{d}$-orbitals can form inner and outer orbital complex depending upon the types of ligands present. It can undergoes hybridisation of type ${\mathrm{sp}}^3$

Hence, option (C) is correct answer. 

$\begin{array}{rl} & \left(\text{e.}\mathrm{g}{\left[{\mathrm{NiCI}}_4\right]}^{2-}\right),{\mathrm{dsp}}^2\left(\text{e.g}{\left[\mathrm{Ni}\right(\mathrm{CN}{)}_4]}^{2-}\right),{\mathrm{sp}}^3{\mathrm{d}}^2\\ & (\text{e.}\mathrm{g}.{\left[{\mathrm{CoF}}_6\right]}^{3-}{\mathrm{d}}^2{\mathrm{sp}}^3{(\mathrm{e}.\mathrm{g}{\left[{\mathrm{NH}}_3\right)}_6]}^{3+}),{\mathrm{dsp}}^3(\mathrm{e}.\mathrm{g}.\left[\mathrm{Fe}\right(\mathrm{CO}{)}_5]\end{array}$