JEE Chemistry 2025 Question with Solution

Given: The metal complex has configuration $t_{2g}^3 e_g^1$.

Find: Which ligand field and spin condition favour this configuration.

In crystal field splitting, the $d$-orbitals split into lower-energy $t_{2g}$ orbitals and higher-energy $e_g$ orbitals. A configuration of $t_{2g}^3 e_g^1$ means one electron occupies the higher-energy $e_g$ level instead of pairing in the lower set.

This is favoured when the crystal field splitting is small, which corresponds to a weak field ligand. The solution states that this configuration is associated with a low spin complex.

Therefore, the correct option is A: Weak field ligand, low spin complex.

Given: The required configuration is $t_{2g}^3 e_g^1$.

Find: The condition that favours this arrangement.

Step 1: In an octahedral metal complex, the $d$-orbitals split into two groups:

Step 2: The configuration $t_{2g}^3 e_g^1$ corresponds to a case where after placing three electrons in $t_{2g}$, the next electron enters $e_g$.

Step 3: the solution explains that when the ligand is weak field, the energy gap between $t_{2g}$ and $e_g$ is relatively small, so occupation of the higher-energy $e_g$ orbital is favoured.

Step 4: The extracted solution concludes that this gives a low spin complex.

Conclude: Hence, the required combination is Weak field ligand, low spin complex, so the correct option is A.