Atomic radius trends
Which atom has the largest atomic radius?
Answer A: explanation for every choice
A
Correct. Potassium is in period 4 and at the left of its period.
B
Sodium is one period above potassium, so it is smaller.
C
Bromine is in period 4 but far to the right, where higher effective nuclear charge pulls electrons in.
D
Chlorine is in period 3, to the right, and is the smallest of these.
TakeawayAtomic radius increases down a group and decreases across a period.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp40.