The O₂ molecule's electron configuration has eight valence electrons in bonding molecular orbitals and four valence electrons in antibonding molecular orbitals, which may be used to compute the bond order. The bond order is thus two.

The fundamental reason oxygen is paramagnetic is because it has two unpaired electrons in its last molecular orbital. If we examine the oxygen molecule's molecular orbital diagram, this may be demonstrated. We can see that oxygen is a diradical with two unpaired electrons with the same spin if we fill each orbital according to Hund's rule.

$\text{ B. }\mathrm{O}$of ${\mathrm{O}}_2^{+}=2.5$(paramagnetic)

Hence correct option is A.