Which of the following methods is not used for preparing a salt?

Options

A. reaction between an acid and a base
B. action of acid on metals
C. action of acid on metal oxides
D. dissolution of acids in water

Explanation

To determine which method is not used for preparing a salt, we can analyze each option provided:

1. **Reaction between an acid and a base**:
- This method is a classic example of a neutralization reaction. When an acid reacts with a base, they produce a salt and water. Therefore, this method is indeed used for preparing a salt.

2. **Action of acid on metals**:
- When an acid reacts with a metal, it produces a salt and hydrogen gas. The reaction typically looks like this:
\[ \text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas} \]
- Hence, this method is also used for preparing a salt.

3. **Action of acid on metal oxides**:
- In this case, when an acid reacts with a metal oxide, it produces a salt and water. The reaction can be represented as:
\[ \text{Acid} + \text{Metal oxide} \rightarrow \text{Salt} + \text{Water} \]
- This method is valid for preparing a salt as well.

4. **Dissolution of acids in water**:
- When an acid is dissolved in water, it simply dissociates into its ions. This process does not produce a salt; it only results in a dilute solution of the acid. Therefore, this method does not lead to the formation of a salt.

Based on the analysis above, the method that is **not** used for preparing a salt is:

**Answer**: Dissolution of acids in water.

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