JEE Main 2026 — 5 April, Evening Shift — Question 58

$\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}$ has oxalate ion as ligand which leads to chelation thus maximum stability among given complexes. (B) Stability : $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}<\left[\mathrm{Cu}(\mathrm{en})_{2}\right]^{2+}$; due to higher CFSE and chelation. (C) $\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$ $\Rightarrow \mathrm{Fe}^{2+}=[\mathrm{Ar}] 3 \mathrm{~d}^{6}$ In presence of SFL the electronic configuration of $\mathrm{Fe}^{+2}\left[\mathrm{t}_{2 \mathrm{~g}}^{6}, \mathrm{e}_{\mathrm{g}}^{0}\right]$, thus $\mathrm{d}^{2} \mathrm{sp}^{3}$ hybridized. (D) $\left[\mathrm{Fe}\left(\mathrm{NO}_{2}\right)_{3} \mathrm{Cl}_{3}\right]^{3-}$ has $\mathrm{NO}_{2}^{-}$as ambidentate ligand thus can show linakge isomerism. (E) $\mathrm{NO}_{2}^{-}$and $\mathrm{SCN}^{-}$both are ambidentate ligands.