Chemistry Atomic Structure UHS 2022
PMDC Verified Question 46 of 95
Which element has the ground state electronic configuration of \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6 \)?
A
\( \text{Na} \)
B
\( \text{Ar} \)
C
\( \text{Cl} \)
D
\( \text{S} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{Ar} \)
Concept: An element's atomic number (number of protons) is equal to its total number of electrons in a neutral, ground-state atom.

Formula: $$ Z = \sum \text{electrons} $$

Solution:
  • Add the superscripts in the given electron configuration to find the total number of electrons:
  • \( 2 + 2 + 6 + 2 + 6 = 18 \) electrons.
  • In a neutral atom, 18 electrons means the atomic number is 18.
  • Looking at the periodic table, element 18 is the noble gas Argon (Ar).


Why other options are incorrect: Sodium (Na) is 11, Chlorine (Cl) is 17, and Sulfur (S) is 16.

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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