Which of the following pairs of compounds are more stable?

Options

A. `K_(2)[NiCl_(6)],[Pt(CN)_(4)]^(2-)`
B. `NiCl_(4),PtCl_(4)`
C. `[Ni(CN)_(4)]^(2-), K_(2)[PtCl_(6)]`
D. `PtCl_(2), NiCl_(2)`

Answer

To determine which pair of compounds is more stable, we need to analyze the oxidation states of nickel and platinum in the given compounds and their corresponding stabilities.

### Step-by-Step Solution:

1. **Identify the Oxidation States**:
- For each compound, we need to determine the oxidation state of nickel (Ni) and platinum (Pt).

2. **Analyze the Stability of Oxidation States**:
- Nickel typically has a +2 oxidation state that is more stable than its +4 oxidation state due to its electron configuration (3d^8 4s^2).
- Platinum, on the other hand, has a +4 oxidation state that is more stable than its +2 oxidation state.

3. **Evaluate the Given Compounds**:
- Let's analyze the pairs of compounds provided in the question:
- **Option 1**: K2NiCl6
- Here, Ni is in +4 state (as deduced from the formula).
- Pt is in +2 state (not suitable).
- **Option 2**: NiCl4
- Ni is in +4 state (not suitable).
- Pt is in +4 state (not suitable).
- **Option 3**: Ni(CN)4^2-
- Here, Ni is in +2 state (as deduced from the formula).
- Pt is in +4 state (suitable).
- **Option 4**: Other combinations
- Both Ni and Pt are in +2 state (not suitable).

4. **Conclusion**:
- The only pair where Ni is in +2 oxidation state and Pt is in +4 oxidation state is found in **Option 3: Ni(CN)4^2-**. This pair is the most stable due to the favorable oxidation states.

### Final Answer:
The most stable pair of compounds is **Option 3: Ni(CN)4^2- (Ni in +2 state and Pt in +4 state)**.

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