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🧪 Chemistry  ·  Solid State  ·  NEET & JEE

Sodium (Na) metal adopts a BCC structure. The number of Na atoms per unit cell is:

Answer: 2.

  • A 1
  • B 2
  • C 3
  • D 4

Correct answer: B. 2

Explanation: BCC has 2 atoms per unit cell: 8 × (1/8) from corners + 1 from the body centre = 2.

Cubic Unit Cells: Atom PositionsSimple CubicCN=6, 52.4% packedBody-Centred (BCC)CN=8, 68% packedFace-Centred (FCC)CN=12, 74% packed (densest)Corner atoms (shared by 8 cells) shown lighter; body/face-centre atoms shown solid

The three cubic unit cells: Simple Cubic has atoms only at corners; Body-Centred adds one atom at the centre; Face-Centred adds one atom at the centre of each of the 6 faces, giving the highest packing efficiency.

Concept context

Explore the ordered world of crystalline solids: unit cells, packing, defects, and how structure determines electrical and magnetic properties.

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