Single correct · +4 / −1
The number of isomers possible for [Co(NH₃)₄Cl₂]³⁺ is:
- (a) 1
- (b) 2
- (c) 3
- (d) 4
Answer and solution
Answer (b) 2
Solution
Chemistry ma’am · 4 steps
Place the two Cl ligands on the octahedron: they can only be next to each other or opposite each other.
- Identify the type. Cobalt has six ligands here, so the complex is octahedral. With four identical NH₃ and two identical Cl, it is an MA₄B₂ complex.
- Place the two Cl. Fix one Cl at any corner. The second Cl goes either at one of the four neighbouring corners (90° apart) or at the single opposite corner (180° apart). All four neighbouring spots give the same structure after a rotation.
Isomer Cl–Co–Cl angle Mirror plane? Optically active? cis (violet) 90° yes no trans (green) 180° yes no - Check optical isomers. Both forms have a mirror plane, so neither has a non-superimposable mirror image. No optical isomers are added.
- So. The complex has exactly 2 isomers, cis and trans. The answer is (b).
The idea to keep. Octahedral MA₄B₂ always gives just cis and trans, and neither is optically active. Fix one ligand and ask where the second can go that a rotation cannot undo.
Answer from the NTA final answer key. Solution by PrepWiser.