Which species has the longest $\mathrm{N}-\mathrm{O}$ bond?

${\mathrm{NO}}_2$ species has the longest N-O bond.
$"\mathrm{B}.\mathrm{O}.:"\mathrm{NO}(2.5),{\mathrm{NO}}^{+}(3.0),{\mathrm{NO}}_2^{+}(2.0)$
The nonlinear molecule ${\mathrm{NO}}_2$ has two bonds that are 1.2 Angstrom long and have a bond angle of 136.4 degrees.
Hence, option C is correct.