Concept:
Crystal structures of metals:
- FCC: Cu, Ni, Ag, Au
- BCC: Na, K, Fe (at room temperature for some phases)
Step 1: Identify structures.
Copper → FCC
Nickel → FCC
Silver → FCC
Step 2: Check sodium.
Sodium is:
\[
\text{BCC (body centered cubic)}
\]
Final Answer:
\[
\boxed{\text{Sodium}}
\]