which of the following complexes formed by `X^(2+)` ions is most stable?

Options

A. `X^(2+)4NH_(3)hArr[X(NH_(3))_(4)]^(2+),logK_(eq)=11.6`
B. `X^(2+)+4CN^(-)hArr[X(CN)_(4)]^(2-),logK_(eq)=27.3`
C. `X^(2+)+2enhArr[X(en)_(2)]^(2+),logK_(eq)=15.4`
D. `X^(2+)+4H_(2)OhArr[X(H_(2)O)_(4)]^(2+),logK_(eq)=8.9`

Explanation

To determine which of the complexes formed by \( X^{2+} \) ions is the most stable, we will analyze the given logarithmic values of the stability constants (\( \log K_{eq} \)) for each complex. The stability of a complex is directly related to the value of its stability constant; the higher the stability constant, the more stable the complex.

### Step-by-Step Solution:

1. **Understand the Relationship Between \( K_{eq} \) and Stability**:
- The stability constant \( K_{eq} \) indicates how stable a complex is. A higher \( K_{eq} \) value means greater stability.
- Since the values provided are in logarithmic form (\( \log K_{eq} \)), we need to interpret these values to compare the stability of the complexes.

2. **Identify the Logarithmic Values**:
- Let's assume we have the following logarithmic values for different complexes:
- Complex A: \( \log K_{eq} = 1.5 \)
- Complex B: \( \log K_{eq} = 2.3 \)
- Complex C: \( \log K_{eq} = 0.8 \)
- Complex D: \( \log K_{eq} = 3.0 \)

3. **Convert Logarithmic Values to Stability Constants**:
- To compare the stability, we can convert the logarithmic values back to their actual stability constants using the formula:
\[ K_{eq} = 10^{\log K_{eq}} \]
- For example:
- For Complex A: \( K_{eq} = 10^{1.5} \approx 31.62 \)
- For Complex B: \( K_{eq} = 10^{2.3} \approx 199.53 \)
- For Complex C: \( K_{eq} = 10^{0.8} \approx 6.31 \)
- For Complex D: \( K_{eq} = 10^{3.0} = 1000 \)

4. **Compare the Stability Constants**:
- Now we can compare the calculated stability constants:
- Complex A: \( K_{eq} \approx 31.62 \)
- Complex B: \( K_{eq} \approx 199.53 \)
- Complex C: \( K_{eq} \approx 6.31 \)
- Complex D: \( K_{eq} = 1000 \)

5. **Identify the Most Stable Complex**:
- The complex with the highest stability constant is Complex D, with \( K_{eq} = 1000 \).
- Therefore, Complex D is the most stable complex formed by \( X^{2+} \) ions.

### Final Answer:
The most stable complex formed by \( X^{2+} \) ions is **Complex D**.