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Question #44551

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The Question

An air-sensitive coordination compound $\mathbf{X}$ has the IUPAC name "Potassium pentacyanidocobaltate(II)". Magnetic measurements reveal a spin-only magnetic moment of approximately $1.73 \text{ BM}$ . Based on Crystal Field Theory and Valence Bond Theory, which of the following correctly identifies the coordination geometry, hybridization of the central metal, and the specific $d$ -orbital containing the unpaired electron for the complex anion?

Options

A.
Square pyramidal, $dsp^3$ , $d_{z^2}$
B.
Trigonal bipyramidal, $sp^3d$ , $d_{x^2-y^2}$
C.
Square pyramidal, $sp^3d$ , $d_{x^2-y^2}$
D.
Trigonal bipyramidal, $dsp^3$ , $d_{xy}$

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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

IUPAC Nomenclature Priority|Spin-Only Magnetic Moment|Valence Bond Theory Hybridization

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to move beyond standard octahedral and tetrahedral geometries.

The hidden trap is the assumption that a coordination number of 5 automatically defaults to a trigonal bipyramidal ( $sp^3d$ ) geometry.

Students must apply Crystal Field Theory to a $d^7$ strong-field case to deduce that square pyramidal geometry is favored.

This geometry leaves the highly destabilized $d_{x^2-y^2}$ orbital empty for inner-orbital $dsp^3$ hybridization, thereby forcing the single unpaired electron into the $d_{z^2}$ orbital.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	IUPAC Nomenclature Priority
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free