Ionization energy is defined as the minimum amount of energy required to remove an electron from an isolated gaseous atom or ion. It is usually measured in kJ/mol or eV/atom. The ionization energy increases as we move from left to right in a period and decreases as we move from top to bottom in a group of the periodic table.



Electron gain enthalpy is defined as the amount of energy released when an electron is added to a neutral gaseous atom to form a negative ion. It is usually measured in kJ/mol or eV/atom. The electron gain enthalpy becomes more negative as we move from left to right in a period and less negative as we move from top to bottom in a group of the periodic table.



Electronegativity is the measure of the ability of an atom to attract the shared pair of electrons towards itself in a covalent bond. Pauling scale is used to measure electronegativity. It ranges from 0.7 to 4.0. The electronegativity of an element can be calculated using the following formula:

Electronegativity = 0.102(sqrt(Ionization energy) + 0.485(Electron gain enthalpy))

where Ionization energy is in kJ/mol and electron gain enthalpy is in kJ/mol.



Given, Ionization energy = 275 kJ/mol and Electron gain enthalpy = -86 kJ/mol

Using the formula, we get:

Electronegativity = 0.102(sqrt(275) + 0.485(-86))

Electronegativity = 2.6

Therefore, the electronegativity of the element on the Pauling scale is 2.6.



The correct option is c. 2.6.

According to Mulliken, electronegativity of an atom is average of ionization energy and electron affinity (in eV). 
nm=IE+EA/2nm=IE+EA2 
If ionization energy and electron affinity are in kcalmol−1−1. 
n=IE+EA125=275+86/125=2.88

Answer is 2.8