Which of the following species has a linear shape?

The nitronium ion (${\text{NO}}_2^{+}$) has 16 valence electrons. The central nitrogen forms two double bonds with oxygen atoms and has zero lone pairs. This results in $sp$ hybridization and a linear geometry with a $180^{\circ }$ bond angle. ${\text{SO}}_2$, ${\text{O}}_3$, and ${\text{NO}}_2^{-}$ all have one lone pair on the central atom and adopt a bent (V-shape) geometry.