Final answer:
Cesium (Cs) has the largest atomic radius among the given elements because it lies at the bottom of Group 1 in the periodic table and has more electron shells.
Step-by-step explanation:
The student asked which of the following atoms has the largest radius: Cs, Ca, O, As, Sn. To find the main answer, we look at the periodic table. Atomic radius generally increases as we move down a group and decreases across a period from left to right. Cesium (Cs) is at the bottom of Group 1, which means it has more electron shells than the other elements listed and thus has the largest radius.
As an explanation, cesium's electrons are further from the nucleus compared to those in calcium (Ca), oxygen (O), arsenic (As), and tin (Sn), which makes Cs atom larger in size. The increase in the number of electron shells as we move down a group outweighs the effect of the increasing nuclear charge, resulting in larger atomic radii.