Question

Given below are two statements :
Statement I : Presence of large number of unpaired electrons in transition metal atoms results in higher enthalpies of their atomisation.
Statement II : $d_{xy} = d_{xz} = d_{yz} < d_{x^2 - y^2} = d_{z^2}$ and $d_{x^2 - y^2} = d_{z^2} = d_{xy} <d_{xz} = d_{yz}$ are the d-orbital splittings in $[Fe(H_2O)_6]^{3+}$ and $[Ni(Cl)_4]^{2-}$ complex ions respectively.
In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

For Statement I, recall how atomization enthalpy varies across the 3d series with the number of unpaired electrons. For Statement II, work out which orbitals point directly at the ligand positions in each geometry, since those are always the higher-energy set, rather than recalling the split pattern from memory.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Statement I relates the strength of metallic bonding to electronic configuration. Statement II concerns the Crystal Field Splitting patterns for octahedral and tetrahedral complexes.
Step 2: Detailed Explanation:
Analysis of Statement I:
Transition metals have unpaired d-electrons which participate in interatomic metallic bonding. The greater the number of unpaired electrons, the stronger the metallic bond, and hence higher is the enthalpy of atomisation. This is True.

Analysis of Statement II:
1. $[Fe(H_2O)_6]^{3+}$ is an octahedral complex. In octahedral field, d-orbitals split into $t_{2g} (d_{xy}, d_{xz}, d_{yz})$ and $e_g (d_{x^2-y^2}, d_{z^2})$. The $e_g$ set is higher in energy. The pattern given ($d_{xy} = d_{xz} = d_{yz}<d_{x^2 - y^2} = d_{z^2}$) is correct.
2. $[Ni(Cl)_4]^{2-}$ is a tetrahedral complex (due to weak field $Cl^-$ ligand). In tetrahedral field, d-orbitals split into $e (d_{x^2-y^2}, d_{z^2})$ and $t_2 (d_{xy}, d_{xz}, d_{yz})$. The $t_2$ set is higher in energy. The second pattern given ($d_{x^2 - y^2} = d_{z^2} = d_{xy}<d_{xz} = d_{yz}$) is incorrect because $d_{xy}$ belongs to the $t_2$ set, not $e$.
Thus, Statement II is Incorrect.
Step 3: Final Answer:
Statement I is correct but Statement II is incorrect.