Chemistry Atomic Structure NUMS 2024
PMDC Verified Question 20 of 95
The element having the electronic configuration of noble gas notation \( \text{(Kr)} 5s^2 4d^6 \) is:
A
\( _{38}\text{Sr} \)
B
\( _{44}\text{Ru} \)
C
\( _{46}\text{Pd} \)
D
\( _{40}\text{Zr} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( _{44}\text{Ru} \)
Concept: To identify an element from its electron configuration, sum the total number of electrons, which equals its atomic number in a neutral state.

Formula: $$ Z = \text{Core electrons} + \text{Valence electrons} $$

Solution:
  • The core is represented by Krypton (Kr). Looking at the periodic table, Krypton has an atomic number of 36. So, there are 36 core electrons.
  • The valence shell adds more: \( 5s^2 \) adds 2 electrons. \( 4d^6 \) adds 6 electrons.
  • Total electrons = \( 36 + 2 + 6 = 44 \).
  • An atomic number of 44 corresponds to Ruthenium (Ru).


Why other options are incorrect: Strontium (Sr) is 38. Palladium (Pd) is 46. Zirconium (Zr) is 40. Only Ruthenium possesses exactly 44 protons.

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