Question

Why nitrogen have a higher ionization enthalpy than that of oxygen?

Answer 1

Nitrogen have a higher ionisation enthalpy then Oxygen due to the presence of a strong
NTripleBondN which makes it difficult for the electrons to break away from the molecule..

Answer 2

nitrogen has high energy of ionisation because of the half-filled 2p orbital which gives nitrogen extra stability, while oxygens tend to easily lose electron because in order to get stable viz to attain half 2p orbital configuration it loses an electron easily