[Co(en)₃]³⁺ does not show optical isomerism.

Solution

Chemistry ma’am · 4 steps

Three en rings wrap around Co like a propeller, and a propeller can twist left or right.

1. Shape of the ion. Each en (ethylenediamine) is a bidentate ligand that spans two adjacent corners of the octahedron. Three of them fill all six positions around Co³⁺, forming three chelate rings.
2. Two twists. The three rings can be arranged like the blades of a propeller turning one way (Δ) or the other way (Λ). These two arrangements are mirror images of each other.
3. Check for symmetry. The ion has no mirror plane and no centre of symmetry, so it is chiral. Its mirror image cannot be placed exactly on top of it, so the Δ and Λ forms are a pair of enantiomers.
4. So. [Co(en)₃]³⁺ does show optical isomerism, so the statement is false.

The idea to keep. Any octahedral complex of the type [M(AA)₃] with three bidentate ligands is chiral and exists as a Δ and Λ pair of enantiomers.

Answer from the NTA final answer key. Solution by PrepWiser.