An example of a double salt is

Options

A. bleaching powder
B. `K_(4)[Fe(CN)_(6)]`
C. `hypo
D. potash alum

Explanation

To determine an example of a double salt, we need to first understand what a double salt is and then evaluate the given options.

### Step-by-Step Solution:

1. **Definition of Double Salt**:
A double salt is a type of salt that contains two different cations or anions in its structure. When dissolved in water, double salts dissociate into their constituent ions, losing their identity as a single compound.

2. **Understanding the Options**:
- **Option A: Bleaching Powder** - The chemical formula is Ca(OCl)₂. This is not a double salt; it is a compound that retains its identity and does not dissociate into two different salts.
- **Option B: K4[Fe(CN)6]** - This is a coordination compound known as potassium ferrocyanide. It does not fit the definition of a double salt because it retains its identity as a coordination complex.
- **Option C: Hypo Solution (Sodium Thiosulfate)** - This is also a coordination compound and does not qualify as a double salt.
- **Option D: Potash Alum (K2SO4·Al2(SO4)3·24H2O)** - This is a classic example of a double salt. It consists of potassium sulfate and aluminum sulfate, and when dissolved in water, it dissociates into its constituent ions.

3. **Conclusion**:
Based on the analysis of the options, the correct answer is **Potash Alum (Option D)**, as it meets the criteria of a double salt.

### Final Answer:
**An example of a double salt is Potash Alum (K2SO4·Al2(SO4)3·24H2O).**