Chemistry S & P Block Elements UHS 2023
PMDC Verified Question 26 of 104
Which of the following has the highest atomic radius in its period?
A
Alkaline earth metals
B
Alkali metals
C
Chalcogens
D
halogens
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Alkali metals
Concept:

Atomic radius is determined by the effective nuclear charge pulling on the valence electron shell.

Solution:

  • As we move from left to right across any given period, the number of protons increases while the valence electrons are added to the exact same shell.
  • This increases the effective nuclear charge, causing the electron cloud to be pulled inward, shrinking the atomic radius across the period.
  • Because they sit at the extreme left (Group 1) of their respective periods, Alkali metals experience the lowest effective nuclear charge.
  • Therefore, they have the most expanded electron clouds and the highest atomic radii in their periods.


Why other options are incorrect:

  • Alkaline earth metals are in Group 2, so they are smaller than Group 1. Chalcogens (Group 16) and Halogens (Group 17) are on the far right and are the smallest in the period (excluding noble gases).

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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