Chemistry Atomic Structure MDCAT 2015
PMDC Verified Question 89 of 95
Which one of the following pairs has the same electronic configuration as possessed by neon (Ne-10)?
A
\( \text{Na}^+, \text{Cl}^- \)
B
\( \text{Na}^+, \text{Mg}^+ \)
C
\( \text{K}^+, \text{Cl}^- \)
D
\( \text{Na}^+, \text{F}^- \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( \text{Na}^+, \text{F}^- \)
Concept: Isoelectronic species have the exact same number of electrons.

Formula: $$ \text{Total Electrons} = Z - \text{Charge} $$

Solution:
  • Neon (Ne) has an atomic number \( Z=10 \), meaning it has 10 electrons.
  • Sodium ion (\( \text{Na}^+ \)): \( Z=11 \), charge = +1 \(\implies 11 - 1 = 10\) electrons.
  • Fluoride ion (\( \text{F}^- \)): \( Z=9 \), charge = -1 \(\implies 9 - (-1) = 10\) electrons.
  • Since both \( \text{Na}^+ \) and \( \text{F}^- \) have 10 electrons, they are isoelectronic with Neon.


Why other options are incorrect: \( \text{Cl}^- \) and \( \text{K}^+ \) have 18 electrons (isoelectronic with Argon), and \( \text{Mg}^+ \) has 11 electrons.

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