According to MO theory how many unpaired electrons are present in O2?

Question

a) 0

b) 1

c) 2

d) 3

e) 4

the answer is 2 but why? please explain will give 5 pts for best answer

Answer 1

There are 8 es to place in 6 MOs. The first 3 (sigma, 2 degenerate pi orbitals) are bonding and take 6 (2 in each orbital) of the 8 electrons of the O2. The other two es occupy the 2 degenerate antibonding pi orbitals. Thus 1e occupies each orbital since the have equal energy