The formula for binary ionic compound formed between cesium and fluorine

Cesium fluoride(CsF)

Explanation:

A binary compound is a compound that is composed of 2 distinct element. An ionic compound is composed of ions, usually one is a metal why the other is a non metal. One element gives out electron to form cation and the other receives electron to form anion in a binary compound.

Cesium is a group 1 element and it has one valence electron and it can easily donate this 1 electron to form a bond with other element. Group 1 element are generally very reactive. Cesium is a metal

Fluorine is in  group 7 of the periodic table and is a non metal .Fluorine have 7 valency electron and requires  1 electron to form a stable octet.

When cesium and fluorine bond to form a binary compound cesium donate 1 electron and fluorine receives the 1 electron for both element to form a stable octet. The formula for the binary ionic compound of cesium and fluorine can therefore be expressed as Cesium fluoride(CsF)