The correct option is B CN–
According to molecular orbital theory (MOT), bond order is given as
bond order = (no. of bonding electrons - no. of antibonding electrons )/2
CN+ : (σ1s)2, (σ∗1s)2, (σ2s)2, (σ∗2s)2, (π2px)2, (π2py)2
bond order = (8-4)/2 = 2
CN : (σ1s)2, (σ∗1s)2, (σ2s)2, (σ∗2s)2, (π2px)2, (π2py)2, (π2pz)1
bond order = (9-4)/2 = 2.5
CN− : (σ1s)2, (σ∗1s)2, (σ2s)2, (σ∗2s)2, (π2px)2, (π2py)2, (π2pz)2
bond order = (10-4)/2 = 3
NO : (σ1s)2, (σ∗1s)2, (σ2s)2, (σ∗2s)2, (π2pz)2, (π2px)2 = (π2py)2, (π∗2px)1 = (π∗2py)0
bond order = (10-5)/2 = 2.5
so, CN− has the highest bond order