Ionisation potential and electron affinity of an element are $17.92 \mathrm{eV}$ and $4.48 \mathrm{eV}$ respectively. The electronegativity of the element on the Pauling scale is _________.

 Electronegativity :The electronegativity of an element can be calculated using the formula:

${\mathrm{Electronegativity}}_{\mathrm{Mulliken}}=\frac{\mathrm{Ionisation} \mathrm{Energy} + \mathrm{Electron} \mathrm{Affinity}}{2}$

The electronegativity on the Mulliken scale is related to the Pauling scale by the mathematical relation:

${\mathrm{Electronegativity}}_{\mathrm{Pauling} \mathrm{Scale}}=\frac{{\mathrm{Electronegativity}}_{\mathrm{Mulliken}}}{2.8}$

Using this relation, and substituting the provided value, we get:

$$\begin{gathered} {\mathrm{Electronegativity}}_{\mathrm{Pauling} \mathrm{Scale}}=\frac{17.92 + 4.48}{2\times 2.8} \\ {\mathrm{Electronegativity}}_{\mathrm{Pauling} \mathrm{Scale}}=\frac{22.4}{5.6} \\ {\mathrm{Electronegativity}}_{\mathrm{Pauling} \mathrm{Scale}}=4 \end{gathered}$$
 

Hence, the required answer is 4.