Chemistry Solids NUMS 2023
PMDC Verified Question 31 of 54
Co-ordination number of \( \text{Na} \) is:
A
10
B
9
C
8
D
12
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 8
Concept:
In metallic solids, the coordination number refers to the number of nearest neighbor atoms immediately surrounding a central atom in the crystal lattice.

Solution:
  • Metallic Sodium (\( \text{Na} \)) crystallizes in a Body-Centered Cubic (BCC) lattice structure.
  • In a BCC arrangement, one atom is located at the center of the cube, surrounded by 8 atoms situated at the corners of the cube.
  • Therefore, the central sodium atom has exactly 8 nearest neighbors touching it.
  • Thus, the coordination number of metallic \( \text{Na} \) is 8.


Why other options are incorrect:
  • A, B: These are not standard coordination numbers for simple cubic lattice systems.
  • D: A coordination number of 12 is found in Close-Packed structures (FCC/HCP), not BCC metals like sodium.

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