one nitrogen bears a positive charge while the other bears a negative charge.
Explanation:
Considering the data stated in the question, the N-N bond is intermediate between a double and a triple bond. A longer bond length means that the bond order will be slightly less than three. The bond may possess more double bond character. Since the N-O bond is slightly shorter than a double bond, the actual bond is intermediate between a single and a double bond. Hence a resonance structure that shows double bonds between the N-N and N-O bonds is likely to be the most stable of all the resonance structures shown.
Finally, as a rule of thumb, resonance structures containing formal charges larger in magnitude than (-1) or (+1) implies that such resonance structure is only a minor contributor. The two other resonance structures are minor contributors to the structure.