Question

Why is the ionisation potential of 'N' is greater than 'O'.

Answer 1

Ionization energy is the minimum energy required to remove the most loosely held electron from one mole of gaseous atoms to produce one mole of gaseous ions each with a charge of .  An atom is highly stable when its valence orbital is completely filled or half-filled and in nitrogen, the valence p orbital is exactly half filled. So, p orbital in nitrogen is more stable than in oxygen, which has one electron more than the half-filled configuration. So, the ionization energy of nitrogen is more than that of oxygen.