Question

which of the following elements has the smallest atomic radius?
sulfur, s
chlorine, cl
selenium, se
bromine, br

Explanation:

Step1: Recall atomic - radius trend

Atomic radius decreases across a period and increases down a group in the periodic table.

Step2: Locate elements in periodic table

Sulfur (S) and chlorine (Cl) are in the third - period, while selenium (Se) and bromine (Br) are in the fourth - period. Since elements in the fourth - period have more electron shells than those in the third - period, Se and Br will have larger atomic radii than S and Cl.

Step3: Compare S and Cl

Among S and Cl, Cl is further to the right in the third - period. As we move from left to right across a period, the effective nuclear charge increases, pulling the electrons closer to the nucleus, and thus decreasing the atomic radius. So, Cl has a smaller atomic radius than S.

Answer:

chlorine, Cl