Question

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

Explanation:

Atomic radius trends: In a period (horizontal row), atomic radius decreases from left to right due to increasing nuclear charge pulling electrons closer. In a group (vertical column), atomic radius increases from top to bottom as there are more electron shells. Chlorine (\(Cl\)) and sulfur (\(S\)) are in period 3. Chlorine is to the right of sulfur, so \(Cl\) has a smaller radius than \(S\). Selenium (\(Se\)) and bromine (\(Br\)) are in period 4. They have an extra electron shell compared to period 3 elements. Among period 4 elements, bromine is to the right of selenium, but still, period 3 elements (like \(Cl\)) have smaller radii than period 4 elements because of the extra shell in period 4. So, comparing all four, chlorine has the smallest atomic radius.

Answer:

chlorine