The pair of compounds having metals in their highest oxidation state is .

Options

A. `MnO_(2) and CrO_(2)Cl_(2)`
B. `[Fe(CN)_(6)]^(3-) and [Cu(CN)_(4)]^(2-)`
C. `[NiCl_(4)]^(2-) and [CoCl_(4)]^(2-)`
D. `[FeCl_(4)]^(-) and Co_(2)O_(3)`

Answer

To determine the pair of compounds having metals in their highest oxidation state, we will analyze each given pair of compounds step by step.

### Step 1: Analyze the first pair - MnO2 and CrO2Cl2

1. **For MnO2:**
- Let the oxidation state of Mn be \( x \).
- Oxygen (O) has an oxidation state of -2.
- The compound is neutral, so:
\[ x + 2(-2) = 0 \]
- Solving this gives:
\[ x - 4 = 0 \implies x = +4 \]

2. **For CrO2Cl2:**
- Let the oxidation state of Cr be \( y \).
- Oxygen (O) is -2 and Chlorine (Cl) is -1.
- The compound is neutral, so:
\[ y + 2(-2) + 2(-1) = 0 \]
- Solving this gives:
\[ y - 4 - 2 = 0 \implies y = +6 \]

### Step 2: Analyze the second pair - Fe(CN)6^3- and Cu(CN)4^2-

1. **For Fe(CN)6^3-:**
- The oxidation state of CN is -1.
- The total charge of the complex is -3, so:
\[ x + 6(-1) = -3 \]
- Solving this gives:
\[ x - 6 = -3 \implies x = +3 \]

2. **For Cu(CN)4^2-:**
- The total charge of the complex is -2, so:
\[ y + 4(-1) = -2 \]
- Solving this gives:
\[ y - 4 = -2 \implies y = +2 \]

### Step 3: Analyze the third pair - NiCl4^2- and CoCl4^2-

1. **For NiCl4^2-:**
- Chlorine (Cl) is -1.
- The total charge of the complex is -2, so:
\[ x + 4(-1) = -2 \]
- Solving this gives:
\[ x - 4 = -2 \implies x = +2 \]

2. **For CoCl4^2-:**
- The calculation is the same as for Ni, so:
\[ y + 4(-1) = -2 \implies y = +2 \]

### Step 4: Analyze the fourth pair - FeCl4^- and Co2O3

1. **For FeCl4^-:**
- The total charge is -1, so:
\[ x + 4(-1) = -1 \]
- Solving this gives:
\[ x - 4 = -1 \implies x = +3 \]

2. **For Co2O3:**
- Let the oxidation state of Co be \( z \).
- Oxygen is -2, and there are 3 O atoms, so:
\[ 2z + 3(-2) = 0 \]
- Solving this gives:
\[ 2z - 6 = 0 \implies z = +3 \]

### Summary of Oxidation States:
- **First Pair:** MnO2 (Mn = +4), CrO2Cl2 (Cr = +6)
- **Second Pair:** Fe(CN)6^3- (Fe = +3), Cu(CN)4^2- (Cu = +2)
- **Third Pair:** NiCl4^2- (Ni = +2), CoCl4^2- (Co = +2)
- **Fourth Pair:** FeCl4^- (Fe = +3), Co2O3 (Co = +3)

### Conclusion:
The pair of compounds having metals in their highest oxidation state is **MnO2 and CrO2Cl2**, with oxidation states of +4 and +6 respectively.