An aqueous solution of potash alum is

Options

A. alkaline
B. acidic
C. neutral
D. soapy to touch

Explanation

### Step-by-Step Solution:

1. **Understanding Potash Alum**:
- Potash alum is a double sulfate salt, typically represented as KAl(SO₄)₂·12H₂O. It consists of potassium ions (K⁺), aluminum ions (Al³⁺), and sulfate ions (SO₄²⁻).

2. **Dissolution in Water**:
- When potash alum is dissolved in water, it dissociates into its constituent ions: K⁺, Al³⁺, and SO₄²⁻.

3. **Hydrolysis of Aluminum Ions**:
- The aluminum ions (Al³⁺) undergo hydrolysis in the aqueous solution. Hydrolysis is the reaction of a substance with water.
- The reaction can be represented as follows:
\[ \text{Al}^{3+} + 6 \text{H}_2\text{O} \rightleftharpoons \text{[Al(H}_2\text{O)}_6]^{3+} \rightarrow \text{[Al(H}_2\text{O)}_5(OH)]^{2+} + \text{H}^+ \]
- In this reaction, aluminum ions attract water molecules, leading to the formation of a complex ion and the release of protons (H⁺) into the solution.

4. **Effect on pH**:
- The release of protons (H⁺) into the solution increases the concentration of hydrogen ions, which lowers the pH of the solution, making it acidic.

5. **Conclusion**:
- Therefore, the aqueous solution of potash alum is acidic in nature due to the hydrolysis of aluminum ions that results in the release of protons.

### Final Answer:
The aqueous solution of potash alum is **acidic** in nature.

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