Chemistry Transition Elements PMC 2021
PMDC Verified Question 36 of 68
Which one of the following has more unpaired electrons?
A
Mn
B
Cr
C
Cu
D
Zn
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Cr
Concept:

To find the number of unpaired electrons, we must write out the electronic configuration for each neutral atom and count the single electrons in the \(s\) and \(d\) orbitals.

Solution:

  • Mn (Z=25): \([Ar] \; 3d^5 \; 4s^2\). The 4s is paired. The 3d has 5 unpaired electrons. Total = 5.


  • Cr (Z=24): \([Ar] \; 3d^5 \; 4s^1\). The 3d has 5 unpaired electrons, and the 4s has 1 unpaired electron. Total = 6.


  • Cu (Z=29): \([Ar] \; 3d^{10} \; 4s^1\). Total = 1.


  • Zn (Z=30): \([Ar] \; 3d^{10} \; 4s^2\). Total = 0.


  • Therefore, Chromium (\(Cr\)) has the highest number of unpaired electrons (6).


Why other options are incorrect:

  • Manganese (\(Mn\)) is a common distractor because its \(d\)-subshell has 5, but its \(s\)-subshell is paired, falling one short of Chromium.

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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