You're right to think Fr (Francium) has the largest atomic radius! Here's why:

* Atomic Radius Trend: Atomic radius generally increases as you move down a group (column) and decreases as you move across a period (row) in the periodic table.

* Francium's Position: Francium is located in the bottom left corner of the periodic table. This means it's in the first group (alkali metals) and the seventh period.

* Reasons for Large Radius:

* More Electron Shells: As you move down a group, atoms gain additional electron shells, effectively increasing the distance between the outermost electrons and the nucleus. Francium has many electron shells.

* Shielding Effect: The inner electrons shield the outer electrons from the full positive charge of the nucleus. This shielding effect is stronger in Francium because of its many electron shells.

* Weak Nuclear Attraction: The nucleus in Francium has a large number of protons, but the outermost electrons are very far away, reducing the attractive force.

In Summary: Francium's position at the bottom left corner of the periodic table, combined with its many electron shells and the shielding effect, results in a very large atomic radius. It's the largest of all the known elements.