Question

Why n2 cation and anion has more and less bond order than neutral n2 molecule?

Answer 1

Go for N2+. 
Base on MO theory. N2 would have a bond order of 3 while N2+ have 2.5. Bond order corresponds usually to the number of bonds. Higher bond order = shorter bond length so, since 2.5 is lesser it has greater bond lenght. That is how I would answer the question...