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 can follow these steps:

### Step 1: Understand Basicity of Metal Hydroxides
Metal hydroxides are basic in nature because they can donate hydroxide ions (OH⁻) in solution. The basicity of a metal hydroxide depends on how easily it can release these hydroxide ions.

**Hint:** Remember that the easier it is for a compound to lose OH⁻ ions, the more basic it is.

### Step 2: Identify the Metals and Their Hydroxides
Let's identify the metal hydroxides we are considering. The common metal hydroxides from the s-block elements include:
- Magnesium hydroxide (Mg(OH)₂)
- Calcium hydroxide (Ca(OH)₂)
- Strontium hydroxide (Sr(OH)₂)
- Barium hydroxide (Ba(OH)₂)

**Hint:** List out the metal hydroxides you are comparing to analyze their basicity.

### Step 3: Analyze the Metal-Oxygen Bond Strength
The basicity can be related to the strength of the metal-oxygen bond in the hydroxide. A stronger bond means that the hydroxide will be less likely to dissociate and release OH⁻ ions.

- **Mg(OH)₂**: Magnesium is a smaller atom, leading to a stronger Mg-O bond.
- **Ca(OH)₂**: Calcium is larger than magnesium, resulting in a weaker Ca-O bond compared to Mg-O.
- **Sr(OH)₂**: Strontium is larger than calcium, leading to an even weaker Sr-O bond.
- **Ba(OH)₂**: Barium is the largest, resulting in the weakest Ba-O bond.

**Hint:** Consider the size of the metal ions; larger metal ions typically form weaker bonds with oxygen.

### Step 4: Compare the Basicity
From the analysis:
- Mg(OH)₂ has the strongest bond and is therefore the least basic.
- Ba(OH)₂ has the weakest bond and is the most basic.
- The order of basicity from least to most basic is:
Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂ < Ba(OH)₂

**Hint:** Remember that the strongest bond corresponds to the least basic hydroxide.

### Step 5: Conclusion
Based on the analysis, we conclude that magnesium hydroxide (Mg(OH)₂) is the least basic among the given metal hydroxides.

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