Electronegativity measures the tendency of an atom in a bond to attract the shared pair of electrons toward itself, and it increases across a period and decreases down a group. Fluorine, situated at the top right of the periodic table among reactive non-metals, has the smallest atomic size and a high effective nuclear charge, giving it the greatest pull on bonding electrons. On the Pauling scale fluorine has the maximum value of 4.0, the highest of any element. Nitrogen (3.0) and oxygen (3.5) lie below fluorine in the same period, while chlorine (3.0) is lower because it is in the next period with a larger size. Thus fluorine has the highest electronegativity. The other options all have smaller values for the reasons given. This ordering is a foundational NCERT periodicity fact. Plausibility check: fluorine forms the most polar bonds and the strongest tendency to draw electrons, fully consistent with it topping the electronegativity scale.