JEE Chemistry 2023 Question with Solution

Given: Four octahedral aqua complexes are given: $\left[\mathrm{Ti(H_2O)_6}\right]^{3+}$, $\left[\mathrm{Cr(H_2O)_6}\right]^{3+}$, $\left[\mathrm{Mn(H_2O)_6}\right]^{3+}$, and $\left[\mathrm{Fe(H_2O)_6}\right]^{3+}$.

Find: Which complex has the highest magnitude of crystal field splitting energy $\Delta_o$.

All the given complexes contain the same ligand, water, so the variation in $\Delta_o$ depends primarily on the metal ion.

For octahedral complexes, higher effective nuclear charge generally increases crystal field splitting. Among the given $+3$ metal ions, $\mathrm{Cr^{3+}}$ has a favorable $d^3$ configuration and stronger metal-ligand interaction.

Therefore, $\left[\mathrm{Cr(H_2O)_6}\right]^{3+}$ has the highest magnitude of octahedral crystal field splitting energy.

The correct option is B.

Given: All complexes have the same ligand $\mathrm{H_2O}$ and the same oxidation state $+3$.

Find: The complex with maximum $\Delta_o$.

Since the ligand is the same in every case, compare only the metal ions. The complex of $\mathrm{Cr^{3+}}$ shows the largest crystal field splitting among the given ions.

Therefore, the correct option is B, that is $\left[\mathrm{Cr(H_2O)_6}\right]^{3+}$.