Which of the following is the most electro-negative element?

The correct answer is Option (3) → Fluorine

Electronegativity is the power of an atom in a molecule to pull the shared pair of electrons towards itself. It rises across a period, as the atoms get smaller and their nuclear charge grows, and falls down a group.

Fluorine, at the top right of the periodic table (leaving out the noble gases), is the most electronegative element, with a value of 4.0 on the Pauling scale; oxygen (3.5), nitrogen (3.0) and hydrogen (2.1) come below it.