Final answer:
Chlorine (Cl) has the smallest atomic radius among the given elements due to the effects of increased nuclear charge and fewer electron shells compared to the others.
Step-by-step explanation:
Based on their positions in the periodic table, we can predict that element Cl (chlorine) has the smallest atomic radius among the given elements: Mg (magnesium), Sr (strontium), Si (silicon), Cl (chlorine), and I (iodine). This is due to the periodic trends that state as we move across a period from left to right, atomic radius decreases due to the increase in the number of protons in the nucleus, which leads to a stronger attraction between the nucleus and the electron clouds, pulling the electrons closer.
Additionally, when moving down a group, atomic radius increases because each row adds a new electron shell, making the atom larger. Since Cl is located to the right of Si on the same period and above I in the same group, it will have a smaller atomic radius than these elements.