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Question #44338

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The Question

An unstable blue-colored complex $\mathbf{P}$ is formed when an acidified aqueous solution of $\ce{K2Cr2O7}$ is treated with $\ce{H2O2}$ . To stabilize $\mathbf{P}$ , the reaction is extracted into an organic solvent like diethyl ether. Upon standing in the aqueous acidic medium, $\mathbf{P}$ spontaneously undergoes an internal redox decomposition to yield a green solution of $\mathbf{Q}$ , along with the evolution of a diatomic gas $\mathbf{R}$ and water.

Determine the correct tuple $(X, Y, Z)$ , where: $X =$ Oxidation state of the central metal in $\mathbf{P}$ . $Y =$ Formal charge on the central metal in the most stable Lewis structure of $\mathbf{P}$ (minimizing formal charge, assuming all bonds are covalent). $Z =$ Number of moles of gas $\mathbf{R}$ evolved per mole of $\mathbf{P}$ completely decomposed.

Options

A.
$(+6, 0, 1.75)$
B.
$(+10, +2, 2.00)$
C.
$(+6, +2, 1.50)$
D.
$(+10, 0, 2.50)$

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

Formal Charge Calculation|Electron Transfer Accounting|KMnO₄ Redox pH Dependency

Why This Question Is Tricky

Common Mistakes

This question tests the critical distinction between Oxidation State (redox bookkeeping assuming ionic bonds) and Formal Charge (Lewis bookkeeping assuming covalent bonds).

Students frequently fall into the trap of calculating the OS of Cr as $+10$ by ignoring the peroxy linkages, or assigning a non-zero FC by misapplying the octet rule to a transition metal.

Furthermore, the decomposition of $\ce{CrO5}$ is a complex internal redox reaction.

A common trap is assuming all peroxy oxygens convert to $\ce{O2}$ (yielding $Z=2$ ), failing to balance the electron transfer where some $\ce{O^{-1}}$ must reduce to $\ce{O^{-2}}$ to satisfy the $3e^-$ requirement of the $\ce{Cr^{+6} -> Cr^{3+}}$ reduction.

Quick Facts About This Question

Question Information

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