JEE Chemistry 2023 Question with Solution

Given: Assertion compares the wavelength of light absorbed by $[CoCl(NH_3)_5]^{2+}$ and $[CoCl(NH_3)_5(H_2O)]^{3+}$. Reason states that absorbed wavelength depends on the oxidation state of the metal ion.

Find: Which option correctly evaluates Assertion and Reason.

For coordination compounds, the absorbed light depends on crystal field splitting energy.

A larger splitting means absorption of higher energy light.

So, larger $\Delta$ implies smaller $\lambda$.

In $[CoCl(NH_3)_5(H_2O)]^{3+}$, the metal is $Co^{3+}$, which has greater crystal field splitting than $Co^{2+}$ in $[CoCl(NH_3)_5]^{2+}$.

Also, $H_2O$ is a stronger field ligand than $Cl^-$, so the splitting in $[CoCl(NH_3)_5(H_2O)]^{3+}$ is further increased.

Therefore, $[CoCl(NH_3)_5(H_2O)]^{3+}$ absorbs shorter wavelength light than $[CoCl(NH_3)_5]^{2+}$.

Hence, the Assertion is false.

The Reason is true because the oxidation state of the central metal ion does affect the splitting and therefore the wavelength of absorbed light.

Therefore, the correct option is D.