To determine which species has a planar triangular shape, we need to analyze the geometry of each option.$\\$1. $N_3^-: \\$• The azide ion $(N_3^-)$ is linear, not planar triangular.$\\$2. $NO_3^-: \\$• The nitrate ion $(NO_3^-)$ has a central nitrogen atom bonded to three oxygen atoms.$\\$• It exhibits resonance and has a trigonal planar geometry.$\\$• The bond angles are approximately $120^\circ. \\$• Therefore, $NO_3^-$ is planar triangular.$\\$3. $NO_2: \\$• The nitrogen dioxide molecule $(NO_2)$ is bent, not planar triangular.$\\$• It has an angle less than $120^\circ$ due to the presence of a lone pair on nitrogen.$\\$4. $CO_2: \\$• The carbon dioxide molecule $(CO_2)$ is linear, not planar triangular.$\\$Based on the analysis, the species with a planar triangular shape is $NO_3^-$.$\\$Thus, the correct option is 2.