Match List - I with List - II. 

Choose the correct answer from the options given below :

For all the complexes in List-I the metal ion is $$Cr^{3+}$$, which has the electronic configuration $$[Ar]\,3d^{3}$$.
Since the oxidation state and the geometry (octahedral) are the same for every complex, the value of the octahedral crystal-field splitting $$\Delta_0$$ depends only on the position of the ligands in the spectrochemical series.

Spectrochemical series (selected ligands, increasing field strength):
$$F^- \lt H_2O \lt en \lt CN^-$$

The stronger the field strength of the ligand, the larger the value of $$\Delta_0$$. Hence the order of $$\Delta_0$$ for the given complexes must follow the reverse of the above sequence:

$$\Delta_0([Cr(CN)_6]^{3-}) \gt \Delta_0([Cr(en)_3]^{3+}) \gt \Delta_0([Cr(H_2O)_6]^{3+}) \gt \Delta_0([CrF_6]^{3-})$$

Comparing with the numerical values supplied in List-II:

26 600 cm⁻¹ > 22 300 cm⁻¹ > 17 400 cm⁻¹ > 15 060 cm⁻¹

We therefore match each complex with the corresponding splitting energy:

A. $$[Cr(CN)_6]^{3-}$$ → 26 600 cm⁻¹ (IV)
B. $$[CrF_6]^{3-}$$ → 15 060 cm⁻¹ (I)
C. $$[Cr(H_2O)_6]^{3+}$$ → 17 400 cm⁻¹ (II)
D. $$[Cr(en)_3]^{3+}$$ → 22 300 cm⁻¹ (III)

Thus the correct set of matches is: A-IV, B-I, C-II, D-III.

Option D which is: A-IV, B-I, C-II, D-III