Final answer:
The atom with the smallest radius is Br. As you move across a period in the periodic table, the atomic radius decreases.
Step-by-step explanation:
The atom with the smallest radius is B (Br). In general, as you move from left to right across a period in the periodic table, the atomic radius decreases. This is because the number of protons in the nucleus increases, resulting in a greater attractive force on the electrons and a smaller atomic radius. Among the options given, Br is the furthest to the right in the periodic table, which means it has the smallest atomic radius.
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