An octahedral complex having molecular composition Co · 5 NH₃ · Cl² . SO₄ has two isomers A and B. The solution of A gives a white precipitate with AgNO₃ solution and the solution of B gives white precipitate with BaCl₂ solution. The type of isomerism exhibited by the complex is,

Solution

Chemistry ma’am · 3 steps

Ask which ion sits outside the bracket: whichever is free is the one that gives the precipitate.

1. Fix the formula. Cobalt is +3 here, five NH₃ are neutral, and one Cl⁻ plus one SO₄²⁻ balance the charge. So the composition is CoCl(SO₄)· 5NH₃ with a single chloride. Five NH₃ fill five of the six octahedral sites, so only one anion can go inside the sphere.

   Isomer	Inside the sphere	Free ion in solution	Test it passes
   A: [Co(NH₃)₅SO₄]Cl	SO₄²⁻	Cl⁻	white AgCl with AgNO₃
   B: [Co(NH₃)₅Cl]SO₄	Cl⁻	SO₄²⁻	white BaSO₄ with BaCl₂

2. Name the swap. A and B have the same formula. A ligand inside the sphere has traded places with the counter ion outside it, so the two compounds release different ions in water. That is ionisation isomerism.
3. So. The complex shows ionisation isomerism, option (b).

The idea to keep. Two isomers that give different precipitate tests are releasing different ions. An anion swapping between ligand and counter ion is ionisation isomerism.

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