Identify the element that has the largest atomic radius on the periodic table

Has the largest atomic number just after the largest noble gas, is a metal. It fits the criteria. Francium has a larger covalent and "Vander Waals" radius than Cesium, but Francium is an extremely unstable element and hence right now the prestige goes to Cesium.

You would do 1500/4 and the answer is 375

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.