Add electron dots and charges as necessary to show the reaction of calcium and oxygen to form an ionic compound Rank these elements according to electronegativity.

1. Neutral Ca atom has 2 valence electrons and gives away those 2 electrons to form Ca²⁺ ion. The neutral O atom has 6 valence electrons and it takes 2 electrons from Ca to form O^2- ion. Thus calcium oxide, CaO is formed.

2. Electronegativity decreases down the group(from top to bottom) and increases along the period from left to right.

out of th given elements, Fluorine is the most electronegative and Cs is the least electronegative . The order of decreasing electronegativity is:

F > C > Al > Na > Cs