JEE Main 2023 — Coordination Compounds Question with Solution

Assertion A : $${\left[\mathrm{CoCl}{\left({\mathrm{NH}}_3\right)}_5\right]}^{2+}$$ absorbs at a lower wavelength of light with respect to $${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\left({\mathrm{H}}_2\mathrm{O}\right)\right]}^{3+}$$.

Given that H₂O is a stronger field ligand than Cl^-, it would result in a larger splitting of the d-orbitals and hence a larger energy difference. This would lead to absorption at a lower wavelength. Therefore, the Assertion A is false.

Reason R : It is because the wavelength of the light absorbed depends on the oxidation state of the metal ion.

While it's true that the oxidation state can influence the absorption wavelength by affecting the energy levels of the d-orbitals, the difference in the absorption wavelength in this specific case is not primarily due to the oxidation state (the oxidation state of Co in both complexes is the same (+3)), but rather due to the difference in ligand field strength (H₂O vs Cl^-). Therefore, the Reason R is not providing the correct explanation for Assertion A.

So, the correct answer would be:

Option A : A is false but R is true.