Which of the following is not a use of baking soda?

Options

A. In medicines as antacid
B. as a component of baking powder
C. in remvoing permanent hardness of water.
D. In fire extinguishers.

Answer

To determine which of the following options is not a use of baking soda (sodium bicarbonate, NaHCO₃), we need to analyze the potential uses of baking soda based on common knowledge and the information provided.

### Step-by-Step Solution:

1. **Identify the Uses of Baking Soda**:
- Baking soda is commonly used in various applications, including:
- As an antacid to relieve heartburn and indigestion.
- As a leavening agent in baking (part of baking powder).
- In some cleaning applications due to its mild abrasive properties.

2. **Examine Each Option**:
- **Option A**: Medicines as antacid.
- Baking soda is indeed used as an antacid. It reacts with stomach acid (HCl) to neutralize it, providing relief from acidity.
- **Option B**: Component of baking powder.
- Baking soda is a key ingredient in baking powder, which is used to help baked goods rise.
- **Option C**: Removing permanent hardness.
- Permanent hardness of water is typically removed using sodium carbonate (washing soda), not baking soda. Baking soda does not effectively remove permanent hardness.
- **Option D**: Fire extinguishing agent.
- Baking soda can be used in fire extinguishers as it releases carbon dioxide when heated, which helps to smother flames.

3. **Conclusion**:
- Based on the analysis, **Option C (removing permanent hardness)** is not a use of baking soda. Instead, it is sodium carbonate that is used for this purpose.

### Final Answer:
**C**: Removing permanent hardness is not a use of baking soda.