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Question #44154

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of $\ce{K2CrO4}$ at $298\text{ K}$ is acidified from $\text{pH} = 10.5$ to $\text{pH} = 1.5$ , converting the major chromium-containing species $P$ to $Q$ . Let $x$ be the maximum number of equivalent $\ce{Cr-O}$ bonds in $P$ , and $y$ be the maximum number of equivalent $\ce{Cr-O}$ bonds in $Q$ . If $d_P$ is the $\ce{Cr-O}$ bond length in $P$ , and $d_{\text{term}}$ and $d_{\text{bridge}}$ are the terminal and bridging $\ce{Cr-O}$ bond lengths in $Q$ respectively, which of the following correctly identifies $x$ , $y$ , and the relationship between the bond lengths?

Options

A.
$x = 4$ , $y = 6$ , and $d_{\text{term}} < d_P < d_{\text{bridge}}$
B.
$x = 4$ , $y = 6$ , and $d_P < d_{\text{term}} < d_{\text{bridge}}$
C.
$x = 4$ , $y = 8$ , and $d_{\text{term}} = d_{\text{bridge}} < d_P$
D.
$x = 4$ , $y = 4$ , and $d_{\text{bridge}} < d_P < d_{\text{term}}$

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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

Bond Order in Resonance Hybrids|Dichromate-Chromate Equilibrium

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of pH-dependent chemical equilibrium, molecular geometry, and resonance theory.

The 'Hidden Variable' is the assumption that dimerization simply links two chromate ions without altering the terminal bond characteristics.

Students often fail to recalculate the resonance hybrid bond orders.

By moving from a system where 2 $\pi$ -bonds are shared among 4 oxygens (B.O. = 1.5) to one where 2 $\pi$ -bonds are shared among 3 terminal oxygens (B.O. = 1.67), the terminal bonds actually become shorter and stronger than the original chromate bonds.

Distractors prey on the assumption that all bonds in dichromate are equivalent or that the terminal bonds weaken upon dimerization.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	Bond Order in Resonance Hybrids
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free