Which element is noted for having the largest atomic radius?

The element with the largest atomic radius is Francium. Atomic radius generally increases as you move down a group in the periodic table and decreases across a period from left to right. This is due to the addition of electron shells as you move down a group, which results in a larger atomic size. Additionally, the increased positive charge in the nucleus as you move across a period causes the electrons to be drawn closer, reducing the atomic radius.

Francium is located in Group 1 (the alkali metals) and is at the bottom of the group. Being further down this group means it has more electron shells compared to other elements listed in the choices, such as Hydrogen, Fluorine, and Oxygen. Hydrogen is a very small atom with only one electron and no other shells; Fluorine, being to the right on the periodic table, has a smaller atomic radius due to the increased nuclear charge pulling its electrons closer; and Oxygen, while larger than Fluorine, still has a smaller atomic radius than Francium due to its higher position in the periodic table. Thus, Francium's position in Group 1 and its status as the heaviest alkali metal contribute to it having the largest atomic radius among the options presented.