Identify the electronegative element in each of the molecules:
a. ch2fcl
b. fch2ch2ch2br
c. hoch2ch2nh2
d. ch3och2li

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