Final answer:
Chlorine(B) has the greatest attraction for electrons due to its higher electronegativity compared to potassium, cobalt, and calcium.
Step-by-step explanation:
The element with the greatest attraction for electrons among potassium (K), chlorine (Cl), cobalt (Co), and calcium (Ca) is chlorine (Cl). Chlorine has a higher electronegativity than the other elements listed, which means it has a greater tendency to attract electrons to itself. Electronegativity increases across a period and decreases down a group in the periodic table. Since chlorine is to the right and above the other elements in the periodic table, it has a higher electronegativity, making it the element with the greatest attraction for electrons.