Explanation

O₂ (oxygen molecule) is paramagnetic because it has unpaired electrons in its molecular orbitals.

According to Molecular Orbital Theory (MOT), the electronic configuration of O₂ reveals 

There are two unpaired electrons in the π* anti-bonding orbitals, which are responsible for its paramagnetic properties.

Hybridization and resonance do not directly explain the presence of unpaired electrons in this context.