Which is the most electronegative element of the periodic table? 

Fluorine 

The correct answer is option 1. Fluorine.

Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. The concept was introduced by Linus Pauling, who devised a scale to quantify electronegativity values for different elements.

Fluorine, located in the top right corner of the periodic table in group 17 (the halogens), has the highest electronegativity of any element. This means that Fluorine has a strong tendency to attract electrons when it forms a chemical bond with other atoms.

The high electronegativity of Fluorine is due to several factors:

1. Atomic Structure: Fluorine has a high nuclear charge (the number of protons in its nucleus) relative to its atomic size. This high positive charge pulls electrons towards the nucleus strongly.

2. Small Atomic Size: Fluorine is a small atom, with a small atomic radius. This means that its valence electrons are close to the nucleus, making it easier for Fluorine to attract electrons.

3. Shielding Effect: The inner electron shells partially shield the outer electrons from the full effect of the nuclear charge. However, in Fluorine, the shielding effect is not as significant due to the small size of the atom, allowing the nuclear charge to have a greater influence on the outer electrons.

Due to its high electronegativity, Fluorine tends to form strong covalent bonds with other elements, particularly hydrogen, oxygen, and carbon. This makes Fluorine an essential element in various industrial and chemical processes, as well as in biological systems.