Explanation:
here's the answer to your question
double arrow just mean that it's a reversible process, and the reaction can go back and forth.
cations are formed when a metal loses electrons, and a nonmetal gains those electrons.
As you progress up any column on the periodic table the atomic radius gets smaller. Fluorine is a very small atom because it has very few electrons and Iodine is a very large atomic radius because it has many electrons.