Question

why nitrogen has less negative electron gain enthalpy than oxygen ?

Answer 1

Nitrogen has half filled electronic configuration 1s²2s²2p³, which is a stable one and it is tough to add one electron. So its having positive electron gain enthalpy. But oxygen has 1s²2s²2p⁴ configuration and is less stable configuration compared to nitrogen. So addition of 1 electron occur and is having negative gain enthalpy.