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🧪 Chemistry  ·  Solid State  ·  NEET & JEE

How many atoms are present per unit cell in a face-centred cubic (FCC) lattice?

Answer: 4.

  • A 1
  • B 2
  • C 4
  • D 8

Correct answer: C. 4

Explanation: FCC: 8 corner atoms (each shared among 8 cells = 1 atom) + 6 face atoms (each shared among 2 cells = 3 atoms); total = 4.

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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