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Question #44340

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The Question

Sodium bismuthate (\ce{NaBiO3}) is a powerful oxidizing agent used in analytical chemistry to quantitatively oxidize \ce{Mn^{2+}(aq)} to \ce{MnO4^{-}(aq)} in an acidic medium at 298 K. Consider the Lewis structure of the bismuthate ion (\ce{BiO3^{-}}) that strictly minimizes formal charges. Let $X$ be the formal charge on the central Bismuth atom in this structure. During the aforementioned redox reaction, Bismuth is reduced to a stable aqueous species where its oxidation state is $Y$ .

Which of the following correctly identifies $X$ , $Y$ , and the primary quantum mechanical driving force for the high thermodynamic oxidizing power of \ce{BiO3^{-}}?

Options

A.
$X = 0$ , $Y = +3$ , Relativistic contraction and stabilization of the $6s$ orbital.
B.
$X = +1$ , $Y = +3$ , Poor shielding by $4f$ and $5d$ electrons increasing effective nuclear charge on $6p$ electrons.
C.
$X = +5$ , $Y = +3$ , Relativistic contraction and stabilization of the $6s$ orbital.
D.
$X = 0$ , $Y = +3$ , High hydration enthalpy of the \ce{Bi^{3+}} ion driving the reduction.

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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

Formal Charge Calculation|Inert Pair Effect|Electron Gain Enthalpy (EGE)

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of Lewis bonding theory and advanced periodic trends.

Students often fall into three traps: 1) Confusing Formal Charge with Oxidation State, leading them to guess $X = +5$ . 2) Applying the strict octet rule (analogous to the isoelectronic nitrate ion) without minimizing formal charge via octet expansion, leading to $X = +1$ . 3) Misunderstanding the quantum mechanical basis of the Inert Pair Effect.

While poor shielding plays a role, the defining feature for the extreme stability of the $6s^2$ pair in period 6 elements is the relativistic contraction of the $s$ -orbital, not the $p$ -orbitals.

The question forces students to reconcile a stable-looking Lewis structure ( $FC=0$ ) with extreme thermodynamic instability.

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