When an ant stings a person, the solution of substance A is rubbed on the stung area of the skin to get relief from pain. The substance A is also used in kitchen for cooking purposes. Another susbtance B is sour in taste and contains an organic acid C. It is used in making pickles. When a solution of A is mixed with B, then a change D takes place to produce bubbles of gas E.
What type of change is D ?

Answer

To solve the question, we need to identify the substances A and B, the change D that occurs when they are mixed, and the type of change that D represents.

### Step-by-Step Solution:

1. **Identify Substance A**:
- The problem states that substance A is used to relieve pain from an ant sting and is also used in cooking. This suggests that substance A is a basic substance.
- The most common substance that fits this description is **baking soda (sodium bicarbonate)**, which has the chemical formula **NaHCO₃**.

2. **Identify Substance B**:
- Substance B is described as sour in taste, contains an organic acid, and is used in making pickles.
- The substance that fits this description is **vinegar**, which primarily contains **acetic acid (CH₃COOH)**.

3. **Identify Change D**:
- When a solution of A (baking soda) is mixed with B (vinegar), a chemical reaction occurs.
- The reaction can be represented as:
\[ \text{NaHCO}_3 + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2 \uparrow \]
- In this reaction, sodium acetate, water, and carbon dioxide gas are produced. The formation of bubbles indicates the release of gas.

4. **Determine the Type of Change D**:
- The change D that occurs when baking soda is mixed with vinegar is a **chemical change**. This is because new substances (sodium acetate, water, and carbon dioxide) are formed during the reaction.

### Conclusion:
The type of change D is a **chemical change**.

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