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Question #44884

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The Question

A purple-colored diamagnetic transition metal complex $\mathbf{A}$ is heated with concentrated $KOH$ to form a green-colored compound $\mathbf{B}$ along with the evolution of $O_2$ gas. Upon altering the pH to a neutral medium, $\mathbf{B}$ undergoes disproportionation to regenerate $\mathbf{A}$ along with a dark brown solid $\mathbf{C}$ . When $\mathbf{C}$ is heated with concentrated $H_2SO_4$ and $NaCl$ , a greenish-yellow gas is evolved, and a soluble manganese salt $\mathbf{D}$ is formed.

Assuming $\mathbf{D}$ exists as a hexaaqua complex in an aqueous solution, what is the spin-only magnetic moment ( $\mu_{eff}$ ) and the Crystal Field Stabilization Energy (CFSE) of the central metal ion in $\mathbf{D}$ ?

Options

A.
$5.92 \text{ BM}, 0 \Delta_o$
B.
$3.87 \text{ BM}, -1.2 \Delta_o$
C.
$0.00 \text{ BM}, 0 \Delta_o$
D.
$1.73 \text{ BM}, -2.0 \Delta_o + 2P$

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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

KMnO₄ Redox pH Dependency|Variable Oxidation State Stability|Magnetic Moment Quenching

Why This Question Is Tricky

Common Mistakes

This problem tests the pH-dependent redox chemistry of $KMnO_4$ and the subsequent isolation of manganese species.

The primary trap lies in the sequential tracking of the oxidation states: students often memorize that $KMnO_4$ is diamagnetic ( $d^0$ ) and might erroneously carry this property forward, or they might fail to identify the complete reduction of $MnO_2$ to $Mn^{2+}$ by $Cl^-$ in acidic conditions, stopping at $Mn^{4+}$ ( $d^3$ , $\mu = 3.87$ BM).

Furthermore, the trap tests Coordination Chemistry by requiring the student to recognize $H_2O$ as a weak field ligand, preventing electron pairing in the $d^5$ system, which results in a CFSE of exactly $0 \Delta_o$ and maximum spin multiplicity.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	D and F Block Elements - Class 12
Concept	KMnO₄ Redox pH Dependency
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free