In which of the following coordmation compounds do the transition metals have an oxidation number of +6?

Options

A. `[Cr(H_2O)_4Cl_2]Cl.2H_2O`
B. `[Fe(CO)_5]`
C. `[(H_2O)_5Cr-O-Cr(H_2O)_5]^(4+)`
D. `K_2[Cr(CN)_2O_2(O_2) NH_3]`

Answer

To determine which coordination compound has a transition metal in the +6 oxidation state, we will analyze each given compound step by step.

### Step 1: Analyze the first compound - \( \text{[Cr(H}_2\text{O)}_4\text{Cl}_2] \)
- **Identify the components**: Chromium (Cr) is the transition metal, and it is coordinated with 4 water molecules (neutral) and 2 chloride ions (each with a -1 charge).
- **Set up the equation**: Let the oxidation state of chromium be \( X \).
\[ X + 4(0) + 2(-1) = 0 \]
This simplifies to:
\[ X - 2 = 0 \implies X = +2 \]
- **Conclusion**: The oxidation state of chromium in this compound is +2.

### Step 2: Analyze the second compound - \( \text{Fe(CO)}_5 \)
- **Identify the components**: Iron (Fe) is the transition metal, and it is coordinated with 5 carbon monoxide (CO) ligands (each neutral).
- **Set up the equation**: Let the oxidation state of iron be \( X \).
\[ X + 5(0) = 0 \]
This simplifies to:
\[ X = 0 \]
- **Conclusion**: The oxidation state of iron in this compound is 0.

### Step 3: Analyze the third compound - \( \text{[Cr(H}_2\text{O)}_5\text{O}]^{2+} \)
- **Identify the components**: Chromium (Cr) is the transition metal, coordinated with 5 water molecules (neutral) and 1 oxygen (O) which is typically -2.
- **Set up the equation**: Let the oxidation state of chromium be \( X \).
\[ X + 5(0) + (-2) = +2 \]
This simplifies to:
\[ X - 2 = +2 \implies X = +4 \]
- **Conclusion**: The oxidation state of chromium in this compound is +4.

### Step 4: Analyze the fourth compound - \( \text{K}_2\text{Cr(CN)}_2\text{O}_2 \)
- **Identify the components**: Chromium (Cr) is the transition metal, coordinated with 2 cyanide ions (each -1) and 2 peroxide ions (each -1).
- **Set up the equation**: Let the oxidation state of chromium be \( X \).
\[ 2(+1) + X + 2(-1) + 2(-1) = 0 \]
This simplifies to:
\[ 2 + X - 2 - 2 = 0 \implies X - 2 = 0 \implies X = +6 \]
- **Conclusion**: The oxidation state of chromium in this compound is +6.

### Final Conclusion
- The only compound where the transition metal has an oxidation state of +6 is \( \text{K}_2\text{Cr(CN)}_2\text{O}_2 \).

### Answer
The correct answer is \( \text{K}_2\text{Cr(CN)}_2\text{O}_2 \).

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