The oxidation number of oxygen in $ Na_2O_2 $ is: · Electrochemistry MDCAT Past Paper MCQ

Chemistry Electrochemistry SZABMU 2024

PMDC Verified Question 7 of 73

The oxidation number of oxygen in $ Na_2O_2 $ is:

-1

-2

Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:

Option A: -1

Concept:

While Oxygen is overwhelmingly found in the $ -2 $ oxidation state, its state changes when it bonds to itself in peroxides ($ O_2^{-2} $).

Formula:

$$2(+1) + 2x = 0$$

Solution:

Sodium (Na) is an alkali metal and unconditionally takes a $ +1 $ oxidation state in its compounds.

Set up the equation for Sodium peroxide ($ Na_2O_2 $): $ 2(+1) + 2x = 0 $.

Solve for $ x $: $ 2 + 2x = 0 \implies 2x = -2 \implies x = -1 $.

Why other options are incorrect:

Oxygen is $ -2 $ in standard oxides (like $ Na_2O $), $ -1/2 $ in superoxides, and only positive when bonded to Fluorine.

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