Chemistry Electrochemistry UHS 2022
PMDC Verified Question 26 of 73
In which of the following, Oxygen shows fractional oxidation number?
A
\( OF_2 \)
B
\( KO_2 \)
C
\( Na_2O_2 \)
D
\( Cl_2O_7 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( KO_2 \)
Concept:

While Oxygen usually has an oxidation state of \( -2 \), its state changes when bonded to more electronegative halogens, or when forming peroxides and superoxides.

Solution:

  • Let's determine the oxidation state of O in Potassium superoxide, \( KO_2 \).


  • Potassium (K) is a Group 1 alkali metal and strictly holds a \( +1 \) oxidation state.


  • Set up the equation: \( +1 + 2x = 0 \implies 2x = -1 \implies x = -1/2 \).


  • The fractional oxidation state of Oxygen in a superoxide is \( -1/2 \).


Why other options are incorrect:

In \( OF_2 \), Oxygen is \( +2 \) (since Fluorine is always \( -1 \)). In Sodium peroxide (\( Na_2O_2 \)), Oxygen is \( -1 \). In Dichlorine heptoxide (\( Cl_2O_7 \)), Oxygen is its normal \( -2 \).

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.

Previous Question All Electrochemistry 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