Which of these molecules is paramagnetic? #"NO"^(-)#, #"O"_2^(2-)#, #"CO"#, or #"CN"^-#?
This is something you know or you don't know. You cannot really work it out from the valence electronic structure.
And thus highest occupied molecular orbitals are the degenerate antibonding orbitals, which are
Note that when we draw an analogous picture for dinitrogen, CONVENTIONALLY,
It would be
Here is a trick to do this question without having to invoke too many MO diagrams, as there is almost no way you could have seen the MO diagram of
(But you're in luck, because I've already drawn it out before if you want to see.)
Basically, know your isoelectronic species:
One of the major breakthroughs of molecular orbital theory was to prove that
As a result,
NITROUS OXIDE ANION