During which one of these processes carried out in a water purification plant does water become colourless?

Options

A. Sedimentation
B. Chlorination
C. Coagulation
D. Filtration

Explanation

### Step-by-Step Solution:

1. **Understanding the Processes**: The question asks about the processes in a water purification plant that can make water colorless. The options given are sedimentation, chlorination, coagulation, and filtration.

2. **Analyzing Each Process**:
- **Sedimentation**: This process involves allowing heavier particles to settle at the bottom of the water body. While it helps in removing some impurities, it does not necessarily make the water colorless.
- **Chlorination**: This is the addition of chlorine to water to kill bacteria and other pathogens. It does not remove color from the water.
- **Coagulation**: In this process, chemicals are added to water to bind small particles together into larger clumps (or flocs) that can then settle out. This may help in reducing color but does not guarantee colorlessness.
- **Filtration**: This process involves passing water through a filter medium that traps solid particles and allows the clear liquid to pass through. As a result, the water becomes colorless as most solids and impurities are removed.

3. **Conclusion**: Among the four processes, filtration is the one that effectively makes the water colorless by removing suspended solids and impurities.

4. **Final Answer**: The correct answer is **Filtration**.