Chemistry S & P Block Elements SZABMU 2022
PMDC Verified Question 53 of 104
Which of the following alkali metal can form normal oxide as well as peroxide?
A
Na
B
K
C
Li
D
Cs
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Na
Concept:

The type of oxide formed by an alkali metal depends heavily on its cationic size and the supply of oxygen during combustion.

Solution:

  • Sodium (Na) is larger than Lithium but smaller than Potassium.
  • When Sodium reacts with a limited supply of oxygen, it forms the normal oxide (\( \text{Na}_2\text{O} \)).
  • When combusted in an excess of oxygen, its size perfectly stabilizes the peroxide ion (\( \text{O}_2^{2-} \)), forming pale yellow Sodium peroxide (\( \text{Na}_2\text{O}_2 \)).
  • Therefore, Sodium is well known for forming both, depending on conditions.


Why other options are incorrect:

  • Li: Extremely small, forms almost exclusively normal oxide (\( \text{Li}_2\text{O} \)).
  • K & Cs: Very large cations, they bypass peroxides and rapidly form superoxides (\( \text{KO}_2, \text{CsO}_2 \)).

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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