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Question #44293

Difficulty: 8/10 | 🟢 Free

The Question

A 3d transition metal $M$ has a ground-state electronic configuration with a completely filled $4s$ orbital. The third ionization enthalpy ( $\Delta_i H_3$ ) of $M$ is anomalously high compared to its adjacent elements because it involves the disruption of a highly stable, exactly half-filled $3d$ subshell.

Finely divided metal $M$ is heated with excess $Cl_2(g)$ at 500 K to yield a binary halide $X$ . The solid $X$ is dissolved in water and treated with an excess of aqueous $KCN$ under an inert atmosphere (absence of air) to form a coordination complex $Y$ .

What is the spin-only magnetic moment of the metal ion in complex $Y$ ?

Options

A.
1.73 BM
B.
2.83 BM
C.
3.87 BM
D.
5.92 BM

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Ionization Enthalpy (IE) Anomalies|Variable Oxidation State Stability|Magnetic Moment Quenching

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of periodic trends (ionization enthalpy anomalies) and coordination chemistry.

Students often falsely assume that transition metals will always form higher oxidation states with excess halogens (e.g., assuming $Mn \rightarrow MnCl_3$ like $Fe \rightarrow FeCl_3$ ).

However, the exceptionally high 3rd IE of Mn (due to the stable $3d^5$ core) restricts it to $MnCl_2$ .

A secondary trap tests Crystal Field Theory: students may erroneously assume that the 'extra stability' of a half-filled $d^5$ subshell prevents pairing even with a strong field ligand like $CN^-$ , leading them to incorrectly choose the high-spin magnetic moment (5.92 BM).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Classification of Elements and Periodicity in Properties - Class 11 Part 1
Concept	Ionization Enthalpy (IE) Anomalies
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free