Final answer:
According to molecular orbital theory, the distribution of the twelve outermost electrons in the O2 molecule is 4 in sigma bonding and 8 in pi bonding. This results in the O2 molecule having two unpaired electrons.
Step-by-step explanation:
According to molecular orbital theory, the twelve outermost electrons in the O2 molecule are distributed as follows: b. 4 in sigma bonding, 8 in pi bonding. In the molecular orbital energy-level diagram for O2, there are only 2 electrons to place in the (p, Tp) pair of orbitals, and according to Hund's rule, one electron occupies each orbital. This results in the O2 molecule having two unpaired electrons.