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Question #44679
The Question
Consider the following three unbalanced redox reactions involving mixed-valence oxides in an acidic medium:
I. II. III.
Let and be the -factors (valency factors) of , , and respectively in the above reactions. Let and be the exact fraction of metal atoms in each respective oxide formula unit that undergo a change in their oxidation state during the reactions.
Calculate the value of the expression:
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Exception_Exposure
Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.
Concepts Behind This Question
Law of Multiple Proportions|Average vs. Actual Oxidation State|Disproportionation Constraints
Why This Question Is Tricky
Common Mistakes
The core trap tests the distinction between 'average' and 'actual' oxidation states in mixed-valence oxides.
Students often rely on the mathematical average (+8/3) to balance redox reactions.
While this works for calculating overall electron transfer (-factor), it completely fails when determining the physical reality of the reaction-specifically, how many atoms actually participate in the electron exchange.
By asking for the fraction of atoms reacting (), the question forces students to recall the exact lattice composition of these spinels and mixed oxides.
Furthermore, it tests periodic trends: and contain +2 and +3 states, whereas contains +2 and +4 states due to the inert pair effect (relativistic s-orbital contraction), making and different despite similar empirical formulas.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Some Basic Concepts of Chemistry - Class 11 Part 1 |
| Concept | Law of Multiple Proportions |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |