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Question #44851

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The Question

Consider the thermodynamic stability of high oxidation state compounds of Group 6 and Group 10 transition metals at $298\text{ K}$ . Which of the following statements correctly identifies the chemical behavior and its primary underlying thermodynamic cause?

Options

A.
$\ce{WF6}$ is thermodynamically more stable than $\ce{CrF6}$ because the sum of the first six ionization enthalpies is lower for $\ce{W}$ than for $\ce{Cr}$ due to its larger atomic radius.
B.
$\ce{PtF6}$ is a stable oxidant while $\ce{NiF6}$ is unknown because the effective nuclear charge ( $Z_{\text{eff}}$ ) of $\ce{Pt}$ is significantly lower than that of $\ce{Ni}$ .
C.
$\ce{CrO_4^{2-}}$ is a stronger oxidizing agent than $\ce{WO_4^{2-}}$ because the high $\ce{W-O}$ bond enthalpies compensate for the higher ionization enthalpies of $\ce{W}$ caused by the lanthanoid contraction.
D.
The stability of maximum oxidation states decreases from $3d$ to $5d$ series because $f$ -orbital contraction drastically reduces the spatial overlap between metal $d$ -orbitals and ligand $p$ -orbitals.

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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

d-orbital contraction|Stability of High O.S. Fluorides/Oxides|Electrode Potential Dependencies

Why This Question Is Tricky

Common Mistakes

This question tests the 'Chemical Exception' regarding the stability of high oxidation states in transition metals.

Students often incorrectly assume that ionization energy decreases down a d-block group (like in the s-block), or they apply the p-block 'inert pair effect' to the d-block.

The trap is failing to recognize that while lanthanoid contraction increases the ionization energy of 5d elements (making electron removal harder), the extended spatial nature of 5d orbitals leads to exceptionally high bond enthalpies with O/F.

This thermodynamic compensation is the true reason why compounds like WF6 and PtF6 are stable, whereas CrF6 and NiF6 are unstable or non-existent.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	D and F Block Elements - Class 12
Concept	d-orbital contraction
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free