JEE Chemistry 2023 Question with Solution

Given: The complex is $[Co(NH_3)_6]^{3+}$.

Find: The hybridization and magnetic behaviour of the cobalt ion in this complex.

Cobalt is in the $+3$ oxidation state, so its electronic configuration is $[Ar]3d^6$. Since $NH_3$ is a strong field ligand, it causes pairing of the $3d$ electrons. Therefore, the complex becomes an inner orbital octahedral complex with hybridization

$$d^2sp^3$$

All electrons are paired, so the complex is diamagnetic.

The solution marks option C as correct, but the extracted option text is inconsistent with the working. The chemically correct description is $d^2sp^3$ and diamagnetic.

Given: $[Co(NH_3)_6]^{3+}$ contains cobalt in the $+3$ state.

Find: Which listed option best matches the actual hybridization and magnetic behaviour.

From the solution:

1. Cobalt in $[Co(NH_3)_6]^{3+}$ is $Co^{3+}$.
2. Its configuration is $[Ar]3d^6$.
3. $NH_3$ is a strong field ligand, so pairing occurs.
4. The complex uses inner orbitals and has

$$d^2sp^3$$

hybridization. 5. Hence all electrons are paired and the complex is diamagnetic.

Therefore, the worked solution supports diamagnetic behaviour with $d^2sp^3$ hybridization. However, none of the listed options states this exactly. Since the solution explicitly declares option C, the answer is recorded as C while noting the mismatch between the options and the explanation.