Why the ionization enthalpy is always positive wehreas electron gain enthalyp can be negative or positive?

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Solution

Dear Student,
The ionization enthalpy is always positive because energy is required to remove an electron from an isolated gaseous atom. Since each electron is associated with a certain energy level so that amount of energy is to be applied to extract the electron.
Electron gain enthalpy can either be positive or negative. Mostly its negative because energy is released when an atom accepts an electron. (H=-ve). In noble gases and certain exceptions the electron gain enthalpy is positive because noble gases have stable octet and elements like N have half - filled subshell , so energy is required to make it accept an electron.
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