Chemistry S & P Block Elements MDCAT 2019
PMDC Verified Question 78 of 104
Ionization energy decrease down the group from top to bottom due to:
A
Decrease in atomic size
B
Increase in atomic mass
C
Increase in shielding effect of the intervening electrons
D
Increase in proton number
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Increase in shielding effect of the intervening electrons
Concept:

Ionization Energy (IE) is the effort required to remove the most loosely bound electron. As we go down a group, this effort consistently decreases.

Solution:

  • Moving down a group, new principal quantum shells are continuously added.
  • These extra inner shells of electrons physically stand between the nucleus and the outermost valence electrons.
  • These intervening electrons repel the valence electrons and block (shield) them from the full attractive force of the nucleus. This is the Shielding Effect.
  • Because of this immense shielding, the nucleus loses its grip on the outermost electrons, drastically lowering the energy required to remove them.


Why other options are incorrect:

  • Option A: Atomic size increases down a group, it does not decrease.
  • Option B & D: Mass and proton number do increase, but increasing proton number alone would actually increase IE if it wasn't overwhelmingly counteracted by the shielding effect.

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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