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

Options

A. `MnO_(2),FeCl_(3)`
B. `[MnO_(4)]^(-),CrO_(2)Cl_(2)`
C. `[Fe(CN)_(6)}^(4-),[Co(CN)_(6)]^(3-)`
D. `[NiCl_(4)]^(2-),[Ni(CO)_(4)]`

Explanation

To determine the pair of compounds that have metals in their highest oxidation state, we will analyze the oxidation states of the metals in each given compound. Here’s a step-by-step solution:

### Step 1: Identify the Compounds and Metals
We need to analyze the oxidation states of the metals in the following pairs of compounds:
1. MnO2 and Fe2O3
2. MnO4^- and CrO2Cl2
3. Fe(CN)6^4- and CoCl3
4. NiCl2 and NiO

### Step 2: Determine the Oxidation States of Metals in Each Compound
1. **MnO2**:
- Oxygen (O) has an oxidation state of -2.
- For MnO2, the total oxidation state must equal 0:
- Mn + 2(-2) = 0 → Mn = +4.

2. **Fe2O3**:
- Oxygen (O) has an oxidation state of -2.
- For Fe2O3, the total oxidation state must equal 0:
- 2Fe + 3(-2) = 0 → 2Fe = +6 → Fe = +3.

3. **MnO4^-**:
- Oxygen (O) has an oxidation state of -2.
- For MnO4^-, the total oxidation state must equal -1:
- Mn + 4(-2) = -1 → Mn - 8 = -1 → Mn = +7.

4. **CrO2Cl2**:
- Oxygen (O) has an oxidation state of -2 and Chlorine (Cl) has an oxidation state of -1.
- For CrO2Cl2, the total oxidation state must equal 0:
- Cr + 2(-2) + 2(-1) = 0 → Cr - 4 - 2 = 0 → Cr = +6.

5. **Fe(CN)6^4-**:
- Cyanide (CN) has an oxidation state of -1.
- For Fe(CN)6^4-, the total oxidation state must equal -4:
- Fe + 6(-1) = -4 → Fe - 6 = -4 → Fe = +2.

6. **CoCl3**:
- Chlorine (Cl) has an oxidation state of -1.
- For CoCl3, the total oxidation state must equal 0:
- Co + 3(-1) = 0 → Co - 3 = 0 → Co = +3.

7. **NiCl2**:
- Chlorine (Cl) has an oxidation state of -1.
- For NiCl2, the total oxidation state must equal 0:
- Ni + 2(-1) = 0 → Ni - 2 = 0 → Ni = +2.

8. **NiO**:
- Oxygen (O) has an oxidation state of -2.
- For NiO, the total oxidation state must equal 0:
- Ni + (-2) = 0 → Ni = +2.

### Step 3: Compare the Oxidation States
- From the analysis:
- Mn in MnO2: +4
- Fe in Fe2O3: +3
- Mn in MnO4^-: +7 (highest oxidation state)
- Cr in CrO2Cl2: +6
- Fe in Fe(CN)6^4-: +2
- Co in CoCl3: +3
- Ni in NiCl2: +2
- Ni in NiO: +2

### Conclusion
The pair of compounds that have metals in their highest oxidation state is **MnO4^- (Mn at +7) and CrO2Cl2 (Cr at +6)**.