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Question #44158

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The Question

Potassium permanganate ( $\ce{KMnO4}$ ) is reduced in a highly alkaline aqueous medium ( $\text{pH} > 13$ ) at $298\text{ K}$ to form a green-colored intermediate species $\ce{X}$ . Upon lowering the $\text{pH}$ to $7$ , $\ce{X}$ undergoes a redox transformation. Based on Molecular Orbital Theory (MOT) and redox principles, which of the following accurately describes the electronic state and stability of $\ce{X}$ ?

Options

A.
$\ce{X}$ is diamagnetic; the HOMO has $t_2$ symmetry, and it is thermodynamically stable at $\text{pH} = 7$ .
B.
$\ce{X}$ is paramagnetic with the unpaired electron in a $t_2$ symmetry orbital; it disproportionates at $\text{pH} = 7$ .
C.
$\ce{X}$ is paramagnetic with the unpaired electron in an $e$ symmetry orbital; it disproportionates at $\text{pH} = 7$ to yield $\ce{MnO4-}$ and $\ce{MnO2}$ .
D.
$\ce{X}$ is paramagnetic with the unpaired electron in an $e$ symmetry orbital; it is stable at $\text{pH} = 7$ due to enhanced $d\pi-p\pi$ bonding.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

MOT and Magnetic Nature|KMnO₄ Redox pH Dependency|Variable Oxidation State Stability

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of Coordination Chemistry/MOT and Redox Chemistry.

Trap 1 (Electronic): Students often default to octahedral crystal field splitting where $t_{2g}$ is lower in energy.

In tetrahedral complexes like $\ce{MnO4^2-}$ , the $e$ set is lower, so the $d^1$ electron resides in an $e$ orbital, not $t_2$ .

Trap 2 (Redox): Students might assume that because $\ce{MnO4^2-}$ is formed via reduction, it represents a universally stable lower oxidation state.

However, its stability is strictly pH-dependent; it is thermodynamically unstable with respect to disproportionation in neutral or acidic media.

The problem filters out rote memorization by demanding the exact orbital symmetry and the specific pH-dependent thermodynamic fate of the intermediate.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	MOT and Magnetic Nature
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free