What is electronegativity?
Answer: It is the tendency of an atom to pull the shared pair of electron towards itself in a covalent bond.
Group 7/17 elements of periodic table are generally electronegative.
The 3 most electronegative elements are FON means Fluorine,Oxygen and Nitrogen.
For Example: H-Cl molecule has polar covalent bond because Cl[chlorine] is more electronegative than H[hydrogen] so Cl pulls the electron pair towards itself and aquire partial negative charge and H acquires partial positive charge.