![Q.23 Upon addition of compound X to an aqueous AgNO₃ solution, a white precipitate appears instantly. Also, X does not exhibit geometrical isomerism. The CORRECT option(s) for X is/are (A) [Cr(OH₂)₄Cl₂]Cl (B) [Cr(OH₂)₅Cl]Cl₂ (C) [Cr(OH₂)₆]Cl₃ (D) [Cr(OH₂)₃Cl₃]](https://www.letstalkacademy.com/wp-content/uploads/2025/12/slide_23-5.png)
Q.23 Upon addition of compound X to an aqueous AgNO₃ solution, a white precipitate appears instantly. Also, X does not exhibit geometrical isomerism.
The CORRECT option(s) for X is/are
Option Analysis
Option (A) [Cr(OH₂)₄Cl₂]Cl
Dissociates as [Cr(OH₂)₄Cl₂]⁺ + Cl⁻, releasing 1 ionizable Cl⁻ that instantly forms white AgCl precipitate with AgNO₃. The [Cr(OH₂)₄Cl₂]⁺ unit (4 H₂O, 2 Cl ligands) in octahedral geometry has cis and trans geometrical isomers (Cl ligands adjacent or opposite), so it exhibits isomerism. Incorrect.
Option (B) [Cr(OH₂)₅Cl]Cl₂
Dissociates as [Cr(OH₂)₅Cl]²⁺ + 2Cl⁻, releasing 2 ionizable Cl⁻ ions for immediate white AgCl precipitate. With only 1 Cl ligand in the coordination sphere (5 identical H₂O + 1 Cl), no geometrical isomerism is possible in octahedral geometry. Correct.
Option (C) [Cr(OH₂)₆]Cl₃
Dissociates as [Cr(OH₂)₆]³⁺ + 3Cl⁻, releasing 3 ionizable Cl⁻ ions that form white AgCl precipitate instantly. All 6 ligands identical (H₂O), so no geometrical isomerism possible. Correct.
Option (D) [Cr(OH₂)₃Cl₃]
No counter ions outside coordination sphere—all 3 Cl are inside, so no ionizable Cl⁻ released and no immediate AgCl precipitate with AgNO₃. The [Cr(OH₂)₃Cl₃] unit shows facial (fac) and meridional (mer) geometrical isomers. Incorrect.
Correct Answer: (B) and (C)
Introduction to Chromium Aqua Chloro Complexes AgNO3 Test
The chromium aqua chloro complexes AgNO3 test identifies ionizable chlorides in coordination compounds by instant white AgCl precipitation. For CSIR NET aspirants, this tests coordination sphere analysis and isomerism. Compounds with Cl⁻ outside the sphere react immediately, while inside Cl ligands don’t.
AgNO3 Test Mechanism
Free Cl⁻ + Ag⁺ → AgCl (white ppt) occurs instantly in aqueous solution. Ionizable Cl (counter ions) precipitate; coordinated Cl (primary/secondary valence) do not dissociate easily. Chromium(III) octahedral complexes [CrL6]³⁺ follow this strictly.
Geometrical Isomerism Rules
Octahedral Ma4b2 shows cis/trans; Ma3b3 shows fac/mer isomers. Ma5b (one B ligand) or Ma6 have no geometrical isomers due to symmetry. Critical for eliminating options in chromium aqua chloro complexes AgNO3 test.
CSIR NET Exam Applications
These isomers distinguish hydrate/ionization isomerism in CrCl3·nH2O series. Practice identifies correct structures for precipitation and isomerism questions. Master for competitive exams!
