The degree of polarity of diatomic molecules is directly related to the difference in

ionization energy

electronegativity

symmetry

neutrons

The correct answer is electronegativity

Explanation:

The tendency of an atom to attract the bonding electron pair towards itself is termed as electronegativity of that atom.

When two atoms forming a covalent bond differs in their electronegativities at time the bonding electrons are not shared equally by both the atoms. This ultimately result in the generation of bond polarity.

For example HCl is a polar bond as H and Cl has huge difference in their electronegativity.