Chemistry Q61 – JEE-MAIN 2026

Home Chemistry Coordination CompoundsQuestion #325

Identify the correct statements from the following A.

[F e (C_{2} O_{4})_{3}]^{3 -}

is the most stable complex among

[F e (O H)_{6}]^{3 -}

[F e (C_{2} O_{4})_{3}]^{3 -}

and

[F e (S C N)_{6}]^{3 -}

. B. The stability of

[C u (N H_{3})_{4}]^{2 +}

is greater than that of

[C u (e n)_{2}]^{2 +}

. C. The hybridization of Fe in

K_{4} [F e (C N)_{6}]

d^{2} s p^{3}

. D.

[F e (N O_{2})_{3} C l_{3}]^{3 -}

exhibits linkage isomerism. E.

N O_{2}^{-}

and

S C N^{-}

ligands are NOT ambidentate ligands Choose the correct answer from the options given below :

Clue 1 of 3: Stability of Complexes and Chelate Effect

Chelating ligands form more stable complexes than monodentate ligands due to the chelate effect.

🧠 Full Solution Path

Step 1: Evaluate Statements A and B (Stability)✦ Active

Statement A: Compare ligands $O H^{-}$ , $C_{2} O_{4}^{2 -}$ (oxalate), and $S C N^{-}$ . Oxalate is a bidentate chelating ligand, while $O H^{-}$ and $S C N^{-}$ are monodentate. Due to the chelate effect, complexes with chelating ligands are more stable. Thus, $[F e (C_{2} O_{4})_{3}]^{3 -}$ is the most stable. Statement A is CORRECT.

Statement B: Compare $N H_{3}$ (monodentate) and $e n$ (ethylenediamine, bidentate chelating). $[C u (e n)_{2}]^{2 +}$ will be more stable than $[C u (N H_{3})_{4}]^{2 +}$ due to the chelate effect. Statement B is INCORRECT.

Step 2: Evaluate Statement C (Hybridization)○ Expand

In $K_{4} [F e (C N)_{6}]$ , the complex ion is $[F e (C N)_{6}]^{4 -}$ . Iron is in the +2 oxidation state ( $F e^{2 +}$ ). The electronic configuration of $F e^{2 +}$ is $[A r] 3 d^{6}$ . Cyanide ( $C N^{-}$ ) is a strong field ligand, causing pairing of electrons in the $3 d$ orbitals. This makes two $3 d$ orbitals available for bonding, leading to $d^{2} s p^{3}$ hybridization. Statement C is CORRECT.

💡 Teacher's Secret Hint

Remember that strong field ligands cause electron pairing in d-orbitals, leading to inner orbital complexes.

Step 3: Evaluate Statements D and E (Isomerism and Ambidentate Ligands)○ Expand

Statement D: Linkage isomerism occurs with ambidentate ligands. $N O_{2}^{-}$ (nitrite) is an ambidentate ligand as it can bind through either nitrogen or oxygen. Therefore, $[F e (N O_{2})_{3} C l_{3}]^{3 -}$ can exhibit linkage isomerism. Statement D is CORRECT.

Statement E: $N O_{2}^{-}$ and $S C N^{-}$ (thiocyanate) are both ambidentate ligands ( $N O_{2}^{-}$ can bind via N or O; $S C N^{-}$ can bind via S or N). The statement claims they are NOT ambidentate, which is false. Statement E is INCORRECT.

Based on the evaluation, statements A, C, and D are correct. This corresponds to option 3.

💡 Teacher's Secret Hint

Recall common ambidentate ligands like $N O_{2}^{-}$ , $S C N^{-}$ , and $C N^{-}$ . They are crucial for linkage isomerism.

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Chemistry Question 61 – JEE-MAIN 2026

Clue 1 of 3: Stability of Complexes and Chelate Effect

🧠 Full Solution Path