Which one is called pseudo solid?

Options

A. `CaF_(2)`
B. Glass
C. NaCl
D. All

Answer

To determine which material is referred to as a pseudo solid, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Pseudo Solid**:
- Pseudo solids are materials that exhibit some characteristics of solids but have the ability to flow like liquids under certain conditions. This means they do not have a definite shape and can deform over time.

2. **Analyze the Given Options**:
- The options provided are:
- a) CaF2 (Calcium Fluoride)
- b) Glass
- c) NaCl (Sodium Chloride)

3. **Evaluate Each Option**:
- **Option a: CaF2**:
- Calcium fluoride is a crystalline ionic solid. Crystalline solids have a fixed structure and do not flow. Therefore, CaF2 cannot be classified as a pseudo solid.

- **Option b: Glass**:
- Glass is an amorphous solid. Amorphous solids do not have a long-range order and can exhibit flow-like behavior over time, especially under stress. Thus, glass can be considered a pseudo solid.

- **Option c: NaCl**:
- Sodium chloride is also a crystalline solid with a well-defined structure (rock salt structure). Similar to CaF2, it does not flow and cannot be classified as a pseudo solid.

4. **Conclusion**:
- Among the options provided, glass is the only material that can be classified as a pseudo solid due to its amorphous nature and ability to flow under certain conditions.

### Final Answer:
- The material that is called a pseudo solid is **glass**.