Question

Oxygen has first electron gain enthalpy exothermic while second is endothermic still a large number of ionic oxides are formed. Why?

Answer 1

This is due to octat rule which is made on the basis of stability.

1. In case of 1st Electron gain enthalpy it forms O- which is less stable then O
2. In case of 2nd EG enthalpy it forms O2- which is more stable then O- and O

It forms large number of ionic states but it depends upon its environment that which one will form the compound.