Which of the following ions forms a hydoxide that is highly soluble in water?

Options

A. `K^(+)`
B. `Zn^(2+)`
C. `Ni^(2+)`
D. `Al^(3+)`

Explanation

To determine which ion forms a hydroxide that is highly soluble in water, we can analyze the given options based on the properties of hydroxides of different elements.

### Step-by-Step Solution:

1. **Identify the Ions**:
- Let's denote the ions as A, B, C, and D. We need to know what these ions are to proceed with the analysis.

2. **Understand Hydroxides**:
- Hydroxides are compounds that contain the hydroxide ion (OH⁻). The solubility of hydroxides in water varies significantly among different elements.

3. **Alkali Metal Hydroxides**:
- Alkali metals (Group 1 elements) form hydroxides that are highly soluble in water. Examples include:
- Lithium hydroxide (LiOH)
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Among these, potassium hydroxide (KOH) is a strong base and is very soluble in water.

4. **Other Metal Hydroxides**:
- Transition metals and some post-transition metals form hydroxides that are generally less soluble in water. For example:
- Nickel hydroxide (Ni(OH)₂) is only slightly soluble.
- Zinc hydroxide (Zn(OH)₂) is also only slightly soluble.
- Aluminum hydroxide (Al(OH)₃) is insoluble in water.

5. **Conclusion**:
- Based on the solubility characteristics, the only ion that forms a hydroxide that is highly soluble in water is the potassium ion (K⁺), which forms potassium hydroxide (KOH).

6. **Final Answer**:
- Therefore, the correct option is **A (K⁺)**.