Question

Why Noble gases have zero electron gain enthalpy?

Answer 1

Noble gases have zero electron gain enthalpy because they contain all paired electrons and there is no place to accept another electron. All the orbitals are completely filled in them. So, they can't accept an electron and so the enthalpy is zero.

Answer 2

Electron gain enthalpy or electron affinity is the amount of energy released when an electron is added to the valence shell of neutral gaseous atom.
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NOBLE OR INERT gases are the elements in which outermost s, p subshells are completely filled.
They belong to 18 group of periodic table.
They are chemically inactive or unreactive as they have stable configuration. So no chance of combining or reacting with other elements, hence no adding of electrons.
Hence electron gain enthalpy is zero.
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