ln which of the following $\mathrm{N}$ atom is not ${\mathrm{sp}}^2$ hybridized?

The Correct option is C.

$\stackrel{\mathit{⊝}}{{\mathrm{NH}}_2}⟶s{p}^3$ hyb. 

$\text{'}\mathrm{N}\text{'}$ atom is ${\mathrm{sp}}^3$ hybridized in ${{\mathrm{NH}}_2}^{-}$.

In ${{\mathrm{NH}}_2}^{-}$molecule, the number of sigma bond is 2 and the number of lone pairs is 2 i.e., ${\mathrm{sp}}^3$ hybridization