Chemistry Solids SZABMU 2024
PMDC Verified Question 8 of 54
Which one of the following is a non-polar molecular solid?
A
\( \text{CO}_2 \)
B
\( \text{SiC} \)
C
\( \text{MgO} \)
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 A: \( \text{CO}_2 \)
Concept:
A molecular solid is non-polar if its constituent molecules possess no net permanent dipole moment (usually due to high structural symmetry cancelling out bond polarities).

Solution:
  • Carbon dioxide (\( \text{CO}_2 \)) has a perfectly linear molecular geometry (O=C=O).
  • Although the individual C=O bonds are polar, they pull exactly in opposite directions, mathematically cancelling each other out.
  • This results in a net dipole moment of zero. Therefore, solid \( \text{CO}_2 \) (dry ice) is a non-polar molecular solid, held together by weak London dispersion forces.


Why other options are incorrect:
  • D: Ice is made of \( \text{H}_2\text{O} \), a bent molecule with a strong permanent dipole, making it a polar molecular solid.
  • C: \( \text{MgO} \) is a lattice of \( \text{Mg}^{2+} \) and \( \text{O}^{2-} \) ions, making it an ionic solid.
  • B: Silicon carbide (\( \text{SiC} \)) is a giant 3D covalent network solid, not molecular.

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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