Identify the one which does NOT belong to the group on the basis of their application in water purification plant.

Options

A. Charcoal
B. Gravel
C. Caum
D. Sand

Explanation

**Step-by-Step Solution:**

1. **Understand the Question**: The question asks to identify which item does NOT belong to the group based on their application in water purification.

2. **List the Given Items**: The items provided are:
- Charcoal
- Gravel
- Alum
- Sand

3. **Analyze Each Item**:
- **Charcoal**: Activated charcoal is commonly used in water purification. It helps to adsorb impurities and contaminants from the water.
- **Gravel**: Gravel is used in water filtration systems. It helps in the settling of larger particles and acts as a support layer for finer filtration.
- **Alum**: Alum is a chemical compound that is used in water treatment to coagulate impurities, but it does not directly purify water by itself. It is more of a coagulant than a purifying agent.
- **Sand**: Sand is used in filtration systems to trap dirt and debris, allowing clean water to pass through.

4. **Identify the Odd One Out**: Based on the analysis, while charcoal, gravel, and sand are directly involved in the physical purification process, alum is primarily a coagulant and does not belong to the same category as the others in terms of direct application in water purification.

5. **Conclusion**: The item that does NOT belong to the group based on their application in water purification is **Alum**.