For ionic equation, the ions that are not involved in the reaction will be deleted. In this equation, the K+ and I- ion are not involved. So the answer should be SO42+(aq) + Ca2+(aq) -> CaSO4(s).
Accordingly the order of electronegativity of the given elements would be: Fluorine > Chlorine > Bromine > Iodine. ( Fluorine has the highest electronegativity.)