Look up the diameters for lithium, sodium, potassium, and cesium atoms. what is the relationship between the atomic number of the element, and the diameter of its atoms? answer

Lithium, sodium, potassium and cesium belong to the same group in the periodic table, together they are called alkali metals. 
As the atomic numbers of these element increase from lithium to cesium, their atomic radii also increase due to increase in the number of valency shells.

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is