By adding gypsum to cement

Options

A. setting time of cement becomes less
B. setting time of cement increases
C. colour of cement becomes light
D. shining surface is obtained

Explanation

### Step-by-Step Solution:

1. **Understanding Cement Composition**: Cement is a key material used in construction, primarily composed of clinker, which is produced by heating limestone and clay in a kiln.

2. **Role of Gypsum**: Gypsum, chemically known as calcium sulfate dihydrate (CaSO4·2H2O), is added to cement during the final grinding process.

3. **Purpose of Adding Gypsum**: The primary reason for adding gypsum to cement is to control the setting time. Without gypsum, cement would set too quickly, making it difficult to work with.

4. **Setting Time of Cement**: The setting time refers to the time it takes for cement to harden after mixing with water. If the setting time is too short, it can lead to weak structures because the cement does not have enough time to gain strength.

5. **Effect of Gypsum on Setting Time**: By adding gypsum, the setting time of cement is increased. This allows for better workability and ensures that the cement can achieve the necessary strength before it hardens completely.

6. **Conclusion**: Therefore, the correct answer to the question "By adding gypsum to cement" is that the setting time of cement increases.

### Final Answer:
**B) Setting time of cement increases.**