Which isomer of `CrCl_3.6H_2O` is dark green in colour and forms one mole of AgCl with excess of `AgNO_3` solution –

Options

A. `[Cr(H_2O)_6]Cl_3`
B. `[Cr(H_2O)_5Cl]Cl_2.H_2O`
C. `[Cr(H_2O)_4Cl_2]Cl.2H_2O`
D. `[Cr(H_2O)_3Cl_3].3H_2O`

Answer

To solve the question regarding the isomer of `CrCl3.6H2O` that is dark green in color and forms one mole of AgCl with excess AgNO3 solution, we can follow these steps:

### Step 1: Understand the Coordination Compound
`CrCl3.6H2O` is a coordination compound where chromium (Cr) is the central metal ion, and it is coordinated with three chloride ions (Cl-) and six water molecules (H2O) as ligands.

### Step 2: Identify Possible Isomers
Chromium(III) chloride hexahydrate can exist in different isomeric forms due to the arrangement of ligands around the chromium ion. The two main types of isomers are:
- **Facial (fac) isomer**: where the same ligands occupy adjacent positions.
- **Meridional (mer) isomer**: where the same ligands are arranged in a plane.

### Step 3: Color of the Isomers
The color of coordination compounds can vary based on the arrangement of ligands and the oxidation state of the metal. The dark green color is typically associated with the fac isomer of `CrCl3.6H2O`.

### Step 4: Reaction with AgNO3
When `CrCl3.6H2O` is treated with excess AgNO3, the chloride ions (Cl-) can react to form silver chloride (AgCl). The formation of one mole of AgCl indicates that there is only one chloride ion that is available for reaction, which is characteristic of the fac isomer.

### Conclusion
The isomer of `CrCl3.6H2O` that is dark green in color and forms one mole of AgCl with excess AgNO3 is the **fac isomer**.

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