`Al_2(SO_4)_3` is used in the following but not

Options

A. as a coagulant in treating drinking water
B. in plastic industry
C. as a mordant in dyeing
D. both C and D

Answer

To solve the question regarding the uses of `Al2(SO4)3` (aluminum sulfate), we will analyze its applications and identify where it is not used.

### Step-by-Step Solution:

1. **Identify the Uses of Aluminum Sulfate**:
- Aluminum sulfate is commonly used in various industries. The primary applications include:
- Water purification: It acts as a coagulant to remove suspended impurities.
- Dyeing: It is used as a mordant to fix dyes on fabrics.
- Paper manufacturing: It helps in sizing paper.
- Food processing: It is sometimes used in pickling.

2. **Analyze the Options Given**:
- The question asks for the application where `Al2(SO4)3` is **not** used. The options provided in the transcript are:
- A) Water purification
- B) Mordant in dyeing
- C) Plastic industry
- D) Both C & D

3. **Evaluate Each Option**:
- **Water purification**: Yes, `Al2(SO4)3` is used here.
- **Mordant in dyeing**: Yes, `Al2(SO4)3` is used here.
- **Plastic industry**: No, `Al2(SO4)3` is not typically used in the plastic industry.
- **Both C & D**: This option includes the previous one, confirming that `Al2(SO4)3` is not used in the plastic industry.

4. **Conclusion**:
- Based on the analysis, the correct answer is that `Al2(SO4)3` is **not used in the plastic industry**.

### Final Answer:
`Al2(SO4)3` is used in water purification and dyeing but **not used in the plastic industry**.