Which of the following elements has the smallest atomic radius?

Periodic trends indicate that atomic radius decreases across a period from left to right due to an increase in effective nuclear charge, and increases down a group due to the addition of electron shells.
* Sodium ($\text{Na}$, Period 3, Group 1) and Chlorine ($\text{Cl}$, Period 3, Group 17): $\text{Cl}$ is smaller than $\text{Na}$.
* Calcium ($\text{Ca}$, Period 4, Group 2) and Bromine ($\text{Br}$, Period 4, Group 17): $\text{Br}$ is smaller than $\text{Ca}$.
* Comparing Chlorine (Period 3) and Bromine (Period 4) in Group 17, Chlorine has fewer shells. Therefore, Chlorine ($\text{Cl}$) has the smallest atomic radius among the given choices.