When a fresh precipitate is turned black in colloidal form, the process is called:

Options

A. Dialysis
B. Coagulation
C. Peptization
D. Electro-osmosis

Answer

To solve the question "When a fresh precipitate is turned black in colloidal form, the process is called:", we need to analyze the options given and understand the concepts related to colloidal chemistry.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a specific process that occurs when a fresh precipitate changes to a colloidal form and turns black.

2. **Reviewing the Options**:
- **Dialysis**: This is a method used to separate colloids from crystalloids by diffusion through a semi-permeable membrane. It is not related to the change of color or form of a precipitate.
- **Coagulation**: This refers to the process where colloidal particles aggregate to form larger particles that settle out as a precipitate. This is the opposite of what we are looking for, as it does not involve turning a precipitate into a colloidal form.
- **Peptization**: This is the process of converting a freshly precipitated solid into a colloidal solution by the action of a peptizing agent (usually an electrolyte). This is the process that can lead to a change in color, such as turning black.
- **Electroosmosis**: This is the movement of liquid through a porous material under the influence of an electric field. It does not pertain to the transformation of a precipitate into a colloidal form.

3. **Identifying the Correct Process**: Among the options, peptization is the correct process that describes the transformation of a freshly precipitated material into a colloidal solution, which can also lead to a color change, such as turning black.

4. **Conclusion**: Therefore, the correct answer to the question is **peptization**.

### Final Answer:
The process is called **peptization**.

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