Chemistry S & P Block Elements MDCAT 2013
PMDC Verified Question 95 of 104
Along a period, atomic radius decreases. This gradual decrease in radius is due to:
A
Increase in number of shells
B
Increase in number of protons in the nucleus
C
Melting and boiling points first decrease then increase
D
Melting and boiling points first increase then decrease
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Increase in number of protons in the nucleus
Concept:

Atomic radius is determined by the balance between the attractive force of the nucleus (protons) and the repulsive force/shielding of the electrons.

Solution:

  • As we move left to right across a period, new electrons are added to the same valence shell (shielding remains relatively constant).
  • However, protons are continuously added to the nucleus.
  • This increases the effective nuclear charge \( (Z_{eff}) \), pulling the electron cloud closer to the nucleus and causing a gradual decrease in atomic radius.


Why other options are incorrect:

  • Option A: The number of shells remains constant along a period.
  • Options C & D: These options were misprinted in the original historical exam paper (they belong to the next question) and have absolutely nothing to do with atomic radius.

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.

Previous Question All S & P Block Elements MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App