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Question #44600

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following coordination complexes at $298\text{ K}$ : (I) \ce{[Ni(CO)4]} (II) \ce{[Fe(CN)6]^{4-}} (III) \ce{[Cu(CN)4]^{3-}} (IV) \ce{[Cr(CO)6]} (V) \ce{[Zn(CN)4]^{2-}} (VI) \ce{[TiF6]^{2-}} (VII) \ce{[Ag(CN)2]^-}

How many of these complexes strictly obey the Effective Atomic Number (EAN) rule (achieving the exact electron count of the nearest noble gas) AND are completely colorless in the visible region specifically due to a $d^0$ or $d^{10}$ electronic configuration (absence of possible $d-d$ transitions)?

Options

A.
2
B.
3
C.
4
D.
5

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

EAN Rule (Sidgwick's Rule)|Color and d-d Transitions|Crystal Field Splitting (Octahedral)

Why This Question Is Tricky

Common Mistakes

This question tests the conceptual boundary between thermodynamic/kinetic stability (EAN rule) and spectroscopic properties (Crystal Field Theory).

Students often conflate a 'full 18-electron shell' with being colorless.

The primary trap is \ce{[Cr(CO)6]}, which obeys the EAN rule and is colorless, but its lack of color is due to a massive $\Delta_o$ pushing the transition into the UV spectrum, not a lack of d-electrons ( $d^6$ ).

The secondary trap involves \ce{[TiF6]^{2-}} and \ce{[Ag(CN)2]^-}, which are colorless due to $d^0/d^{10}$ configurations but fail to reach the nearest noble gas electron count, punishing students who only check for color and ignore the strict EAN calculation.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	EAN Rule (Sidgwick's Rule)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free