Question

Why is electron affinity positive. And why is electron affinity the negative of electron gain enthalpy?

Answer 1

Dear Student,
Electron Gain enthalpy is the energy released when an isolated gaseous atom accepts an electron to covert into an anion.

... Electron affinity, a property of an atom in isolated atom should be defined at absolute aero only. This value is positive
if energy is released and negative, if energy is utilised.
The concept of both the properties are same but they have opposite signs.

 1).If the energy is released on adding an e- to the gaseous atom,then e- affinity is taken as positive. ...

2).If the energy has to be supplied when an e- is added then e- affinity is taken as negative. ​​​​​​​Regards