Metals form basic hydroxides. Which of the following metal hydroxide is the least basic?

Options

A. `Mg(OH)_(2)`
B. `Ca(OH)_(2)`
C. `Sr(OH)_(2)`
D. `Ba(OH)_(2)`

Explanation

To determine which metal hydroxide is the least basic among the given options, we need to analyze the basicity of metal hydroxides based on the strength of the metal-oxygen (M-O) bond. The basicity of a metal hydroxide is inversely related to the strength of this bond: stronger bonds lead to lower basicity because the hydroxide ion (OH⁻) is less likely to be released.

### Step-by-Step Solution:

1. **Understand Basicity**: Basicity of metal hydroxides is determined by how easily the hydroxide ion (OH⁻) can be released. If the M-O bond is strong, the hydroxide ion is held tightly and is less likely to dissociate, resulting in lower basicity.

2. **Consider Metal Size and Bond Strength**: The size of the metal ion affects the bond length and strength. Smaller metal ions (like magnesium) form shorter and stronger M-O bonds, while larger metal ions (like barium) form longer and weaker M-O bonds.

3. **Analyze the Given Metals**:
- **Magnesium Hydroxide (Mg(OH)₂)**: Magnesium is a small metal ion, leading to a strong M-O bond and thus lower basicity.
- **Calcium Hydroxide (Ca(OH)₂)**: Calcium is larger than magnesium, resulting in a weaker M-O bond and higher basicity than magnesium.
- **Strontium Hydroxide (Sr(OH)₂)**: Strontium is larger than calcium, leading to an even weaker M-O bond and higher basicity than calcium.
- **Barium Hydroxide (Ba(OH)₂)**: Barium is the largest among these metals, resulting in the weakest M-O bond and the highest basicity.

4. **Conclusion**: Based on the analysis, magnesium hydroxide (Mg(OH)₂) has the strongest M-O bond and thus is the least basic among the given options.

### Final Answer:
**Magnesium Hydroxide (Mg(OH)₂)** is the least basic metal hydroxide.

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