Stability of benzene, polycylic aromatic and aromatic compounds is directly proportional to the resonance energy per ring. The resonance energy of benzene is 36 kcal/mol, naphthalene is 30.3 kcal/mol, and anthracene is 28 kcal/mol.Therefore, the order of stability is, Benzene > phenanthrene > naphthalene > anthracene.