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Electronegativity is theability of an atom in a chemical compound to attract a bond pair of electronstowards itself.
Electronegativity of anygiven element is not constant. It varies according to the element to which itis bound. It is not a measurable quantity. It is only a relative number.
Onthe other hand, electron gain enthalpy is the enthalpy change that takes placewhen an electron is added to a neutral gaseous atom to form an anion. It can benegative or positive depending upon whether the electron is added or removed.An element has a constant value of the electron gain enthalpy that can bemeasured experimentally.