The formal charges possible on three$\mathrm{N}$-atoms in an ${\mathrm{N}}_3^{-}$ molecule is/are: [If $\mathrm{N}$ atoms are connected in the sequence $\mathrm{N}-\mathrm{N}-\mathrm{N}$]

Formal charge= (Number of valence ${\mathrm{e}}^{-}$ in a free neutral atom) −21​(Number of bonding${\mathrm{e}}^{-}$) − (Number of nonbonding ${\mathrm{e}}^{-}$)

Using the above equation we can calculate the formal charge on

$\mathrm{N}\equiv {\mathrm{N}}_{+1}^{\oplus }-{\mathrm{N}}_{{ }^{-2}}^{2-};{\mathrm{N}}_{-2}^{2-}-{\mathrm{N}}_{+1}^{\oplus }=\underset{0}{\mathrm{N};}{\mathrm{N}}_{-1}^{-1}={\mathrm{N}}_{+1}^{\oplus }={\mathrm{N}}_{-1}^{-1}$

Hence, the correct option is (a, c, d).