Hint: Electronegativity relates to the ease with which an atom can attract a shared pair of electrons in a covalent compound.
Complete answer: > Electronegativity is defined as the tendency of the atom of an element in a chemical compound to attract a shared pair of electrons towards it in a covalent bond. Since electronegativity is just a tendency, it is a dimensionless quantity. > A number of electronegativity scales are present. These include Pauling scale, Milliken-Jaffe scale, Allred Kochow scale etc. Out of these scales, Pauling scale is usually used in which fluorine (the most electronegative element) was arbitrarily assigned a value of 4.0. Least electronegative element cesium is assigned a value of 0.7. > Electron gain enthalpy is closely related to electron affinity but significantly differs from electronegativity. > Electron gain enthalpy is defined as the enthalpy change when a neutral gaseous atom takes up an extra electron to form an anion. > Electron gain enthalpy is the tendency of an isolated gaseous atom to accept an additional electron to form a negative ion. Electronegativity is the tendency of the atom of an element in a chemical compound to attract a shared pair of electrons towards it in a covalent bond. > Electronegativity is a qualitative measure. It is not a measurable quantity. However, electron gain enthalpy is a quantitative measure. It is a measurable quantity.
Note: In a period, on moving from left to right, with increase in the atomic number, the nuclear charge and the electronegativity increases. In a group, on moving down, with increase in the atomic number, the effective nuclear charge decreases due to an additional shell of electrons. Hence, electronegativity decreases.