Difference in density is the basis of

Options

A. Ultrafiltration
B. Molecular sieving
C. Gravity separation
D. Molecular attraction

Answer

To solve the question "Difference in density is the basis of," we will analyze the options provided and determine which one is primarily based on the principle of density differences.

### Step-by-Step Solution:

1. **Understanding the Options**:
- The options given are: ultrafiltration, molecular sieving, gravity separation, and molecular attraction.
- We need to identify which of these processes relies on the difference in density.

2. **Analyzing Gravity Separation**:
- Gravity separation, also known as hydraulic washing, is a method that separates particles based on their specific gravity.
- In this process, powdered ore is washed over an inclined surface with water flowing through it.
- The heavier particles (ore) settle down due to gravity, while the lighter particles (gangue or impurities) are washed away.

3. **Examining Ultrafiltration**:
- Ultrafiltration involves passing a liquid through a semi-permeable membrane.
- This process separates particles based on size rather than density. Heavier solutes remain on one side of the membrane, but this is not primarily based on density.

4. **Considering Molecular Sieving**:
- Molecular sieving uses materials with uniform pore sizes to separate particles based on size.
- Similar to ultrafiltration, this method does not primarily rely on density differences but rather on the size of the molecules.

5. **Looking at Molecular Attraction**:
- Molecular attraction refers to the forces between charged particles (positive and negative).
- This method does not involve density differences but rather electrostatic forces.

6. **Conclusion**:
- The only process among the given options that is based on the difference in density is **gravity separation**.
- Therefore, the answer to the question is **gravity separation**.

### Final Answer:
**Difference in density is the basis of gravity separation.**