The amorphous form of silica is

Options

A. kieselguhr
B. tridymite
C. cristobalite
D. quartz

Explanation

To solve the question "The amorphous form of silica is," we need to analyze the given options: Geiselgau, Tridymite, Cristobalite, and Quartz.

### Step-by-Step Solution:

1. **Understanding Silica Forms**:
- Silica (SiO2) can exist in various forms, primarily as crystalline and amorphous. The crystalline forms have a well-defined structure, while the amorphous forms do not.

2. **Analyzing Quartz**:
- Quartz is a crystalline form of silica with a well-defined arrangement of atoms. Its chemical formula is SiO2. Since it has a defined structure, it cannot be classified as an amorphous form.

3. **Analyzing Cristobalite**:
- Cristobalite is another crystalline form of silica. It has the same chemical formula (SiO2) as quartz but a different crystalline structure. Like quartz, it has a well-defined arrangement, so it is not amorphous.

4. **Analyzing Tridymite**:
- Tridymite is also a crystalline form of silica. It is found in a hexagonal crystal shape and, similar to quartz and cristobalite, possesses a well-defined arrangement. Therefore, it is not an amorphous form.

5. **Identifying the Amorphous Form**:
- The option Geiselgau (which is likely a misspelling of "Kieselguhr") refers to a form of amorphous silica. Kieselguhr is composed of the silica shells of unicellular aquatic plants and does not have a well-defined arrangement, making it the correct answer.

### Conclusion:
The amorphous form of silica is **Kieselguhr** (option A).

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