Step 1: Recall what electronegativity means.
It tells how strongly an atom pulls the shared electrons of a bond towards itself. A bigger pull means a higher value.
Step 2: Use the periodic trend.
The pull grows as you move across a period to the right, and it drops as you go down a group. So the strongest pullers sit at the top right of the table, leaving out the noble gases.
Step 3: Compare the choices.
Out of fluorine, chlorine, oxygen and nitrogen, fluorine sits highest and farthest right. It holds the top spot for electronegativity in the whole table.
\[ \boxed{\text{Fluorine}} \]