Does NO2- or NO3- have a greater bond length??

Answer 1

NO3- has a greater bond length.
For both ions, all N-O bonds are equivalent due to resonance.
For both ions you have in the resonance structures 1 double bond.
For NO2- you have also 1 single bond. Thus the 2 N-O equivalent bonds are a mix of 1 double and 1 single bond, thus they are approximately of 1.5 order.
For NO3- you have 2 single bonds (apart for the double bond). Thus the 3 N-O equivalent bonds are a mix of 1 double and 2 single bonds. Thus the multiple bond character is lower and thus the length is greater.

Answer 2

NO2 has greater bond length.

Answer 3

Former