'Alum' is an example of

Options

A. single salt
B. double salt
C. acids
D. none of above

Explanation

**Step-by-Step Solution:**

1. **Understanding Alum**: The term 'alum' refers to a specific type of chemical compound that is commonly known as a double salt.

2. **Definition of Double Salt**: A double salt is a compound that consists of two different cations or two different anions. In the case of alum, it contains two different types of cations.

3. **General Formula of Alum**: The general formula for alum can be represented as M2SO4·M'2(SO4)3·24H2O. Here, M represents a univalent cation (like potassium), and M' represents a trivalent cation (like aluminum).

4. **Example of Alum**: A common example of alum is potash alum, which has the chemical formula K2SO4·Al2(SO4)3·24H2O. In this formula, K (potassium) is the univalent cation and Al (aluminum) is the trivalent cation.

5. **Conclusion**: Since alum contains two types of cations, it is classified as a double salt.

**Final Answer**: Alum is an example of a double salt.

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