Step 1: Understanding the Concept
In a bcc unit cell, atoms touch along the body diagonal.
Body diagonal \(=\sqrt{3}\,a=4r\).
Step 2: Calculation
\(r=\dfrac{\sqrt{3}\,a}{4}=\dfrac{1.732\times 522}{4}\).
Step 3: Result
\(r\approx 226\) pm.
Final Answer:
The radius of the potassium atom is about 226 pm.
\[ \boxed{\text{(B) }226\ \text{pm}} \]