Cobalt chloride when dissolved in water forms pink colored complex `X` which has octahedral geometry. This solution on treating with conc.HCl forms deep blue complex, `Y` which has a `Z` geometry. `X,Y` which has a `Z` geometry. `X,Y` and `Z,` respectively,are

Options

A. `X=[Co(H_2O)_4Cl_2]^+ ,Y=[CoCl_4]^(2-)`,Z=Tetrahedral
B. `X=[Co(H_2O)_6]^(2+) ,Y=[CoCl_6]^(3-)`,Z=Octahedral
C. `X=[Co(H_2O)_6]^(2+) ,Y=[CoCl_4]^(2-)`,Z=Tetrahedral
D. `X=[Co(H_2O)_6]^(3+) ,Y=[CoCl_6]^(3-)`,Z=Octahedral

Answer

To solve the problem step by step, we need to analyze the information given about cobalt chloride and the complexes formed when it is dissolved in water and treated with concentrated hydrochloric acid.

### Step 1: Identify the Complex X
Cobalt chloride (CoCl₂) when dissolved in water forms a pink-colored complex. The formula for this complex can be represented as:
\[ \text{[Co(H}_2\text{O)}_6]^{2+} \text{Cl}_2^{-} \]
This complex has an octahedral geometry due to the presence of six water molecules (ligands) surrounding the cobalt ion.

### Step 2: Identify the Complex Y
When the complex X is treated with concentrated hydrochloric acid (HCl), it forms a new complex. The reaction can be represented as:
\[ \text{[Co(H}_2\text{O)}_6]^{2+} + 4 \text{Cl}^- \rightarrow \text{[CoCl}_4]^{2-} + 6 \text{H}_2\text{O} \]
This complex, Y, is deep blue in color and has the formula:
\[ \text{[CoCl}_4]^{2-} \]
The geometry of this complex is tetrahedral because it has four chloride ions as ligands.

### Step 3: Determine the Geometry Z
From the information provided, we know that:
- Complex X is \(\text{[Co(H}_2\text{O)}_6]^{2+}\) (octahedral).
- Complex Y is \(\text{[CoCl}_4]^{2-}\) (tetrahedral).
- The geometry Z is the same as that of complex Y, which is tetrahedral.

### Conclusion
Thus, we can summarize:
- Complex X: \(\text{[Co(H}_2\text{O)}_6]^{2+}\) (pink, octahedral)
- Complex Y: \(\text{[CoCl}_4]^{2-}\) (blue, tetrahedral)
- Geometry Z: Tetrahedral

### Final Answer
The complexes X, Y, and their respective geometries Z are:
- X: \(\text{[Co(H}_2\text{O)}_6]^{2+}\) (octahedral)
- Y: \(\text{[CoCl}_4]^{2-}\) (tetrahedral)
- Z: Tetrahedral