Step-by-step explanation:
The periodic table
Periodic Trends: Electron Affinity
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Chlorine is an element that is less electronegative than oxygen, but it has the highest electron affinity of any element.
Affinity can refer to the tendency of an atom to combine by chemical reaction with atoms or compounds or the electronic property by which dissimilar chemical species are capable of forming chemical compounds.
Answer: Cl and because of its highest electron affinity.