Question

The correct pair in which both the complex ions show the ground state electronic degeneracy is

• A. [TiF$_6$]$^{2-}$ and [Ti(H$_2$O)$_6$]$^{2+}$
• B. [Fe(CN)$_6$]$^{4-}$ and [Mn(CN)$_6$]$^{3-}$
• C. [Ti(H$_2$O)$_6$]$^{2+}$ and [Mn(CN)$_6$]$^{3-}$
• D. [Fe(CN)$_6$]$^{4-}$ and [TiF$_6$]$^{2-}$

Hint:

Electronic degeneracy occurs when d-orbitals are partially filled (not $d^0$ or $d^{10}$)Always check oxidation state and ligand field strength

Answer 1

The Correct Option is C

Step 1: When degeneracy appears.
A ground state is orbitally degenerate when the lower t$_{2g}$ set is unevenly filled.

Step 2: Test the ions.
[Ti(H$_2$O)$_6$]$^{2+}$ is d$^2$ with t$_{2g}^2$, which is degenerate. [Mn(CN)$_6$]$^{3-}$ is low spin d$^4$ with t$_{2g}^4$, also degenerate.

Step 3: Rule out the rest.
[TiF$_6$]$^{2-}$ is d$^0$ and [Fe(CN)$_6$]$^{4-}$ is low spin d$^6$ with a filled t$_{2g}$, so neither is degenerate.

Step 4: Answer.
\[ \boxed{[\text{Ti(H}_2\text{O)}_6]^{2+} \text{ and } [\text{Mn(CN)}_6]^{3-}} \]