Chemistry Solids SET 2019
PMDC Verified Question 49 of 54
In diamond each of the four outer electrons on every carbon atom is involved in covalent bonding. This means that there are no free electrons available. Which of the following property is explained by this statement?
A
Diamond does not conduct heat and electricity
B
Diamond is very hard
C
Diamond has high refractive index
D
Diamond cuts diamond
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Diamond does not conduct heat and electricity
Concept:
Electrical and thermal conductivity in solids primarily depend on the availability of mobile (free) charge carriers, such as delocalized electrons.

Solution:
  • In diamond, every carbon atom is \( \text{sp}^3 \) hybridized and covalently bonded to four other carbon atoms.
  • Because all four valence electrons are locked into strong, localized sigma bonds, there are absolutely zero free electrons available to carry a charge.
  • Therefore, the lack of free electrons directly explains why diamond is a non-conductor of electricity (and fundamentally limits electronic heat conduction).


Why other options are incorrect:
  • B, D: The hardness of diamond is explained by the rigid, 3D tetrahedral network of strong covalent bonds, not just the lack of free electrons.
  • C: The refractive index is related to optical density and the rigid lattice, not directly to conductivity.

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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