Describe a simple test to account for differences in electronegativity between 2 atoms

The electronegativity of an atom represents the tendency that it has to attract electrons towards itself when combined with another element. It serves to predict the type of bonds. F being the most electronegative element has a lot of ability to attract electrons to itself, so also being a very small element in terms of radius also has a lot of ionization energy if we compare it with the Fr which the atomic radius is very large, It does not need much energy to release the electron however it has very low affinity.

Explanation:

The scale to establish the electronegative was created by the chemist Pauling who established a scale of 0.7 in the least electronegative atoms to 4, the most electronegative. In this case the Fluor.

the answer is 0.42 is that is an option. this question provides no info