Chemistry S & P Block Elements SZABMU 2023
PMDC Verified Question 31 of 104
Among alkali metals which element reacts slowly with \( \text{H}_2\text{O} \)?
A
Na
B
K
C
Rb
D
Li
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Li
Concept:

The reactivity of alkali metals with water is directly related to their ionization energy and how easily they can lose their valence electron.

Solution:

  • Reactivity in Group 1 increases as you move down the group.
  • Lithium (Li) is at the very top of Group 1. It has the smallest atomic radius and the highest ionization energy among the alkali metals.
  • Because its nucleus holds onto the valence electron more tightly, it takes more effort to lose it.
  • As a result, Lithium reacts relatively slowly and steadily with water (it effervesces, releasing hydrogen gas, but does not melt or explode like the others).


Why other options are incorrect:

  • Na, K, and Rb are lower in the group. Their larger sizes make them lose electrons far more easily, causing them to react violently and explosively with water.

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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