To determine the hybridization of the nitrogen atom in different species, we need to understand the underlying principles of hybridization. Hybridization involves the mixing of atomic orbitals to form new hybrid orbitals, which explain the molecular geometry of covalent compounds.
Thus, the nitrogen atom in NO_2^+ exhibits sp hybridization, making this the correct answer.
Hybridisation and geometry of [Ni(CN)$_4$]$^{2-}$ are