JEE Chemistry 2025 Question with Solution

Given: We need to identify the coordination complexes in which the central metal ion has a $d^4$ configuration.

Find: The correct option containing the complexes with central metal ions of configuration $d^4$.

To identify the coordination complexes in which the central metal ion has a $d^4$ configuration, examine the electronic configuration of the central metal ions in each complex.

For (A) $[FeO_4]^{2-}$: iron is in the $+6$ oxidation state. The electronic configuration of Fe is $[Ar] \, 3d^6 4s^2$. In the $+6$ state, it loses $6$ electrons, leaving a $d^2$ configuration.

Therefore, this does not match $d^4$.

For (B) $[Mn(CN)_6]^{3-}$: manganese is in the $+3$ oxidation state. The electronic configuration of Mn is $[Ar] \, 3d^5 4s^2$. With a $+3$ charge, it loses $3$ electrons, resulting in a $d^4$ configuration.

Therefore, this matches $d^4$.

For (C) $[Fe(CN)_6]^{3-}$: iron is in the $+3$ oxidation state. The configuration of Fe is $[Ar] \, 3d^6 4s^2$. Losing $3$ electrons leaves a $d^5$ configuration.

Therefore, this does not match $d^4$.

For (D) $Cr_2(O - C(Me)_4(H_2O)_2$: each Cr is in the $+2$ oxidation state. The configuration of Cr is $[Ar] \, 3d^5 4s^1$. Losing $2$ electrons results in a $d^4$ configuration.

Therefore, this matches $d^4$.

For (E) $[NiF_6]^{2-}$: nickel is in the $+4$ oxidation state. The configuration of Ni is $[Ar] \, 3d^8 4s^2$. Losing $4$ electrons results in a $d^6$ configuration.

Therefore, this does not match $d^4$.

So, the complexes with $d^4$ configuration are (B) and (D) only.

Therefore, the correct option is C.

Given: We must determine which listed complexes have a central metal ion with a $d^4$ electronic configuration.

Find: Which combination of complexes corresponds to $d^4$.

A $d^4$ configuration means the metal ion has $4$ electrons in the $d$-orbitals after accounting for its oxidation state.

• (A) $[FeO_4]^{2-}$ gives iron in a state that leads to $d^2$, so it is not correct.
• (B) $[Mn(CN)_6]^{3-}$ contains $Mn^{3+}$, which is $d^4$, so it is correct.
• (C) $[Fe(CN)_6]^{3-}$ contains $Fe^{3+}$, which is $d^5$, so it is not correct.
• (D) chromium complex has chromium in a state leading to $d^4$, so it is correct.
• (E) $[NiF_6]^{2-}$ does not give a $d^4$ configuration, so it is not correct.

Thus, only (B) and (D) satisfy the required condition.

The correct option is C.