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Ionization Enthalpy is the amount of energy required to remove an electron from the outer most shell of an isolated gaseous atom.

Electron affinity is the amount of energy released when one electron is gained by an ion or atom.

\(Cl \longrightarrow Cl ^{-} \text {E.A.=-X }\)

\(Cl ^{-} \rightarrow Cl\, I.E. \,=+X\)

Thus, magnitude of \(I.E.\) and \(E.A.\) is same for the above process because same amount of energy is required or released to add an electron in \(Cl\) or to remove an electron from \(Cl ^{-}\).

Thus, \(\mid\, I.E.\) of process\((ii) \,|=| \,E.A.\) of process\((i)\,\mid\)