Colloids can be purificed by

Options

A. Tyndal effect
B. Coagulation
C. Peptization
D. Ultrafiltration

Explanation

To solve the question "Colloids can be purified by?", we need to analyze the given options and determine which one is a valid method for purifying colloidal solutions.

### Step-by-Step Solution:

1. **Understanding the Options**:
- **A. Tyndall Effect**: This refers to the scattering of light by small particles in a colloid. It is not a method of purification but rather a phenomenon that helps identify the presence of colloidal particles.
- **B. Coagulation**: This is the process where colloidal particles aggregate to form larger particles. While it can change the state of the colloid, it does not purify it; instead, it may remove the colloidal state.
- **C. Peptization**: This is the process of converting a precipitate into a colloidal solution by adding a suitable electrolyte. It does not purify colloids but rather helps in the formation of colloidal solutions.
- **D. Ultrafiltration**: This is a method that uses special filters to separate colloidal particles from soluble impurities. It effectively purifies colloidal solutions by removing unwanted substances.

2. **Identifying the Correct Method**:
- From the analysis, we see that options A, B, and C do not serve as methods for purifying colloids. They either describe phenomena or processes that do not lead to purification.
- Option D (Ultrafiltration) is the only method that specifically addresses the purification of colloids by separating them from impurities.

3. **Final Answer**:
- Therefore, the correct answer is **D. Ultrafiltration**.