Answer
B
Work Step by Step
Nitrogen has 7 electrons in total, oxygen has 8.
Configuration:
$\sigma_{1s}\ \sigma_{1s}^*\ \sigma_{2s}\ \sigma_{2s}^*\ 3×\sigma_{2p}\ 3×\sigma_{2p}^*$
There are 10 electrons in bonding orbitals and 5 in antibonding so:
$B.O.=(N.\ Bonding -N.\ Antibonding)/2$
B.o. = 5/2=2.5