Chemistry Solids BUMHS 2023
PMDC Verified Question 27 of 54
Which one of the following have no cleavage plane?
A
Graphite
B
\( \text{NaCl} \) crystals
C
Copper crystals
D
Ice
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Copper crystals
Concept:
Cleavage is the tendency of a crystalline solid to split cleanly along definite, flat structural planes when struck.

Solution:
  • Ionic and covalent network solids often have distinct planes of weakness where they can snap or cleave cleanly (e.g., \( \text{NaCl} \) or graphite).
  • However, Copper is a metallic crystal.
  • Metals consist of a flexible, non-directional "sea of electrons" surrounding positive metal cores. Because metallic bonds are non-directional, properties remain the same in all directions.
  • When struck, instead of cleaving, the planes of atoms simply slide past one another without breaking the continuous metallic bond. This makes copper malleable and ductile, meaning it lacks distinct cleavage planes.


Why other options are incorrect:
  • A, B, D: Graphite cleaves easily between its sheets, \( \text{NaCl} \) cleaves along its cubic faces, and ice also has structural cleavage planes due to rigid hydrogen bond networks.

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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