Chemistry - Coordination Chemistry Question with Solution | TestHub

Option A (Correct): As the negative charge on the metal increases ($[Fe{]}^{2-}$ > $[Co{]}^{-}$ > $[Ni{]}^0$), back-bonding to CO increases. This weakens the C–O bond, decreasing its stretching frequency (${\nu }_{CO}$); thus, $[Ni(CO{)}_4]$ has the highest frequency.

Option B (Incorrect): Both complexes follow the EAN rule, having an EAN of 36 (Kr configuration), so the "greater than" sign is incorrect.

Option C (Incorrect): Trien (triethylenetetramine) is tetradentate, while imda²⁻ (iminodiacetate) is tridentate; the denticity order is reversed.

Option D (Correct): $[Ni(en{)}_3{]}^{2+}$ has 2 stereoisomers (an enantiomeric pair $d$ and $l$), while $[Ni(N{H}_3{)}_2(en{)}_2{]}^{2+}$ has 3 (the trans-form is achiral, and the cis-form exists as $d$ and $l$ isomers).