Here's why:
* Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond.
* Chlorine is located in the upper right corner of the periodic table, which is where the most electronegative elements reside.
* Electronegativity generally increases across a period (from left to right) and decreases down a group (from top to bottom). This means that chlorine, being higher up and further to the right than sulfur and selenium, will have a stronger pull on electrons.
Therefore, chlorine has the greatest electronegativity out of the three elements.
