First electron affinity of oxygen is negative but second electron affinity is positive-explain.

Explanation

When an electron is added to valency shell of an isolated gaseous O-atom in its ground state to form a uninegative ion, energy is released, because neutral oxygen atom tends to complete its octet with electrons. So, electron affinity of oxygen is an exothermic process and its value is negative when an extra electron is added to `O^(-)` ion, that second electron experiences a force of repulsion exerted by the negative charge of the anion. so, first this process requires supply of energy from an external source. this accounts for the endothermic nature of second electron affinity and it has a positive value.