Chemistry Solids SZABMU 2024
PMDC Verified Question 5 of 54
\( \text{NaCl} \) is an example of ____ arrangement of crystal lattice.
A
Monoclinic
B
Octahedral
C
Tetrahedral
D
Triangular
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Octahedral
Concept:
The coordination geometry of an ionic lattice describes the spatial arrangement of nearest neighbor ions around a central ion.

Solution:
  • In a Sodium Chloride (\( \text{NaCl} \)) crystal, the lattice is face-centered cubic (FCC).
  • Within this FCC lattice, every single \( \text{Na}^+ \) ion is surrounded by six \( \text{Cl}^- \) ions located along the x, y, and z axes (up, down, left, right, front, back).
  • Geometrically, if you connect the centers of these 6 surrounding chloride ions, it forms an eight-faced shape called an octahedron.
  • Therefore, \( \text{NaCl} \) exhibits an octahedral arrangement.


Why other options are incorrect:
  • A: Monoclinic is a crystal system shape, not the localized atomic coordination arrangement for \( \text{NaCl} \).
  • C: Tetrahedral arrangement implies a coordination number of 4 (like in Zinc Blende, \( \text{ZnS} \)), whereas \( \text{NaCl} \) is 6.
  • D: Triangular implies a 2D planar coordination of 3, which is incorrect for 3D salt lattices.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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