(a, d)
(a) Electronic configuration of N2=σ1s2, σ*1s2, σ2s2, σ*2s2, π2px2≈π2py2, σ2pz2
It has no unpaired electron indicates diamagnetic species.
(b) Electronic configuration of N2-2 ion=σ1s2, σ*1s2, σ2s2, σ*2s2, π2px2≈π2py2, σ2pz2, π*2px1≈π*2py1
It has two unpaired electrons, paramagnetic in nature.
(c) Electronic configuration of O2=σ1s2, σ*1s2, σ2s2, σ*2s2, σ2pz2, π2px2≈π2py2, π*2px1≈π*2py1
The presence of two unpaired electrons shows its paramagnetic nature.
(d) Electronic configuration of O2-2 ion=σ1s2, σ*1s2, σ2s2, σ2pz2, π2px2≈π2py2, π*2px2≈π*2py2
It contains no unpaired electron, therefore, it is diamagnetic in nature.