Why does Oxygen have a lower first ionization energy then nitrogen?

Why does oxygen have a lower first ionization energy than nitrogen?

• Answer:

  Nitrogen -Electron configuaration[He]2s22p3 has three electrons in individual 2p orbitals with aligned spins because electrons try and stay as far apart as possible. Oxygen -Electron Configuration -[He]2s22p4 must put 2 electrons in a 2p orbital with opposite spins. This causes a slight repulsion between these electrons which is greater than electrons in separate orbitals making this electron slightly easier to remove. in nitrogen ,there are 3 electrons in outer shell i.e., it is half filled orbital and it required more energy to remove one electron because it is in stable state.But it in oxygen an electron can be easily removed.