Question

which of the following elements has the smallest atomic radius?
chlorine
sulfur
bromine
selenium

Explanation:

Atomic radius decreases across a period (from left to right) due to increasing nuclear charge which pulls electrons closer. Chlorine (\(Cl\)) and sulfur (\(S\)) are in period 3, bromine (\(Br\)) and selenium (\(Se\)) in period 4. Period 4 elements have larger radii as they have an extra electron shell. Among \(Cl\) and \(S\), \(Cl\) is further right (group 17 vs. group 16 in period 3), so it has a smaller atomic radius.

Answer:

chlorine