Electronegativity means how strongly an atom can attract electrons. The more positive charge an atom has, the better it attracts the negatively charged electrons. However, distance is a factor too, so if the nucleus (where the protons are) starts becoming too large, the strength of the positive charge isn't as large as it would otherwise be.
Basically this means that fluorine is the most electronegative element since it has the most positive charge for its relative size. Elements closer to fluorine have higher electronegativities than elements further from it on the periodic table.
so in other words F is most electro, bc it attracts more electrons to its atom making other atoms Positive
