Which of the following is/are preferred resonating structure of azide ion ${\mathbf{N}}_3^{-}$? 

The preferred resonating structure of azide ion ${\mathbf{N}}_3^{-}$

Because  ${\mathbf{N}}_3^{-}$ allows for the drawing of four resonance structures, only three are actually feasible because the N in structure IV's rightmost end does not meet the requirements for an octet configuration.