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 are substances A ?

Answer

To solve the question step by step, let's analyze the information provided and deduce the substances involved.

### Step 1: Identify Substance A
- The question states that Substance A is used to relieve pain from ant stings and is also used in cooking.
- A common household item that fits this description is **baking soda** (sodium bicarbonate, NaHCO₃). It is often used for its basic properties to neutralize the acidic venom from ant stings and is also a common ingredient in cooking.

### Step 2: Identify Substance B
- The question mentions that Substance B is sour in taste, contains an organic acid, and is used in making pickles.
- A well-known substance that is sour and used in pickling is **vinegar**, which contains **acetic acid** (C₂H₄O₂).

### Step 3: Identify the Reaction
- When Substance A (baking soda) is mixed with Substance B (vinegar), a chemical reaction occurs.
- The reaction can be represented as:
\[ \text{NaHCO}_3 + \text{C}_2\text{H}_4\text{O}_2 \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2 \]
Here, sodium acetate (CH₃COONa), water (H₂O), and carbon dioxide (CO₂) are produced.

### Step 4: Identify the Changes
- The change that occurs when baking soda and vinegar are mixed is a **chemical change** (Change D), resulting in the formation of new substances (sodium acetate, water, and carbon dioxide).
- The bubbles of gas produced (Gas E) are due to the release of carbon dioxide.

### Final Answer
- Therefore, Substance A is **baking soda (NaHCO₃)**.