Chemistry S & P Block Elements ETEA 2023
PMDC Verified Question 35 of 104
Choose the element that forms normal oxide only:
A
Li
B
Na
C
K
D
Rb
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Li
Concept:

The formation of peroxides and superoxides requires a large metal cation to stabilize the large, complex oxygen anions via lattice energy matching.

Solution:

  • Lithium (Li) is the smallest of the alkali metals.
  • It possesses a very high charge density, which creates an intensely strong lattice energy when paired with the small oxide ion (\( \text{O}^{2-} \)).
  • If Lithium were to pair with a large peroxide or superoxide ion, the lattice would be highly unstable.
  • Therefore, when burned in air, Lithium reacts almost exclusively with oxygen to form only the normal oxide (\( \text{Li}_2\text{O} \)).


Why other options are incorrect:

  • Na: Forms peroxides (\( \text{Na}_2\text{O}_2 \)).
  • K & Rb: Are large enough to easily form superoxides (\( \text{KO}_2, \text{RbO}_2 \)).

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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