Chemistry S & P Block Elements DUHS 2023
PMDC Verified Question 42 of 104
Which pair of the element markedly differ from other members of the respective groups?
A
Potassium and Calcium
B
Sodium and Magnesium
C
Cesium and Barium
D
Lithium and Beryllium
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Lithium and Beryllium
Concept:

The first element of s and p block groups often displays anomalous behavior compared to the rest of its group due to its exceptionally small size and high charge density.

Solution:

  • Lithium (Li) is the first member of Group I, and Beryllium (Be) is the first member of Group II.
  • Because they are located at the very top of their groups, they have incredibly small atomic and ionic radii.
  • This results in anomalously high ionization energies and high polarizing power (charge-to-size ratio).
  • Consequently, Li and Be form bonds with significant covalent character, whereas the rest of their group members form purely ionic compounds.
  • Therefore, the pair Lithium and Beryllium shows peculiar behavior that markedly differs from the larger metals below them.


Why other options are incorrect:

  • Na/Mg, K/Ca, and Cs/Ba exhibit standard, predictable metallic and ionic behaviors typical of the lower periods of their groups.

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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